Paul, FWIW I think your approach is a good one. Except for outright competition, cycling should include an element of fun to be satisfying long-term. That said, randonneuring/Audax is one of the more enjoyable forms of "sportive" cycling as there is a sort of low-key competitive element and most of that is self-competition and goal-reaching. There is a "first finisher" but no "winner" in the usual sense so that takes some pressure off. Of course, some commitment is necessary if you wish to climb the ladder to meet the requirements for, say, Paris-Brest-Paris. That requires you ascend past the 400km rides to the Super-Randonneur events and that takes a chunk of training time and commitment. I think you have to also be in the headspace to do it and I am not. 400km is my upper limit as beyond that seems pointless
for me compared to other forms of cycling I prefer more for enjoyment and, yes, fun. And, too, as I have progressed through Life some of my priorities have changed and I am now less driven to the extremes of accomplishment than when I was younger.
It
is easy to get hung-up on the numbers/distances involved with randonneuring/Audax, but in the end it is just a long(er) bike ride than usual and you can either do it on your own (as I most often do) or as part of an organized event with others, as George (mickeg) has done.
The good news about the formal events is they tend to have pretty generous time limits so it is fairly easy to come in under the cutoff...or if you go alone, to practice hitting the mark and I'd recommend that first before formally signing-on for an event. By practicing in your own, you'll gain experience and build a mileage base for the real thing, all pressure-free. Official average speeds as determined by cutoffs move right along but aren't super-fast. As I recall, the Audax maximum time allowance for the 200km is 13 hours 30 minutes, and for the 400km is 27 hours. That's a 14.8kmh (9.19mph) average. Longer distances have even lower averages based on more generous time allowances. A 1200km super-randonneur has a 90 hour limit making for a 13.3kmh average (8.28mph). That doesn't mean one actually travels that slow when riding. What it means is it allows for rest breaks, toilet stops, food intake and, yes, naps along the way. Your average is 0 while off the bike, so any stop chips away at the average. This is one reason why I generally take food to nibble on while I ride, so I can avoid stopped time off the bike (or make it count with a refreshing nap).
On windless flats when in good condition, I can hum along in a window between 27-33.8kmh (17-21mph). Each hour I do that counts for about two hours' riding at the minimum speed, so I can build up a "cushion" that allows for stops or mishaps like unexpected repairs or naps.
I find it helps to become familiar with doing quick TSD -- Time, Speed, Distance -- calculations in the back of my mind as I ride along so I now how I'm keeping pace. Yes, my computers have Average Speed and even pacing arrows to let me know if I'm on track or need to hurry things up a bit, but I find it helpful to have some idea myself. Obvious, but I'll point it out anyway: Randonneur/Audax cutoff times are based on Average Overall including stops. Many computers only display a Running Average based on actual time and distance and go to sleep or stop recording when you stop. These tend to be more common and if you have one, be sure to keep that in mind as I once got caught out as more time had actually slipped by than I realized. An aside...I once got my hands on a rally-specific Halda Tripmaster, a mechanical rally-specific TSD calculator. Such fun! A day went by before I came up for air. It was eclipsed by the SpeedPilot I saw later. Google the names if you're interested in learning more about an essential tool that was key to classic rallying back in the day.
Dunno if it might help to share my general training strategy, but here goes...
If I take the calendar year as a start, in January I make sure I start putting in time and distance on my Fixie as I find it refines my form and builds fitness the fastest. I typically start by working up to consistent 100km ceilings, adding not distance but hills as I grow more fit. Once I hit the 100km mark with ease and regularity, I switch to my geared bikes and build in increments so I am comfortably able to do each level 10-15 times before moving up a notch. For me, comfortable increments are 113km, 150km, and then 200km. I stick at 200km pretty consistently for awhile and then find I can pop up to 250 and then 300 more easily building on that 200km base. The stretch from 300-400km is always a big one for me not so much because of the distance, more because by necessity it takes me into much more demanding terrain (unless I want to do endless loops in low-altitude farmland...okay once in awhile but boring for me after the second time around).
I try to get in my highest mileage rides between early July and late September, simply because I have an adequate training base by then to make them relatively easier and injury-free.
I sure don't do 400km rides very often because they do require an extra time commitment for training and preparation and as mentioned before, it is a LOT of riding in the dark. I don't mind night rides as part of a tour of starting early/coming into camp late, but much of my enjoyment while riding comes from the scenery and when it is really dark, that is limited to a pretty small cone of light so I don't see very much and find that disappointing and, frankly, unfulfilling for the amount of effort I'm putting in. I'd rather turn the same distance into a mini-tour of 12 hours' riding each day with an overnight in my tent midway before the turnaround or to sleep at 200 as a springboard for subsequent days' rides, as when I need to get from my home in Oregon's southern Willamette Valley to Northern California or Nevada pretty quickly. This also means I maximize daylight so I can take photos and enjoy the scenery along the way.
When you do the longer rides that go into night, it helps to have a lighted display on your navigation equipment. For awhile, I rigged a small button cell-powered LED aimed at the screen on my wired bike computer. As I recall, SIGMA made one for awhile that zip-tied to the handlebars and shone on the display when desired. If you have a Garmin-type sat-nav/computer combo, then I'd suggest placing some small squares of self-adhesive glow-in-dark tape on or by the switches to prevent fumbling for them. I did that with my Edge Touring and found it helpful. Be sure to toss in a wearable LED headlight in case you have to make repairs or fix a puncture in the dark. Cyclists generally have pretty good muscle memory for those things but it sure is faster if you can see! Also, take more spare tubes than you expect (i.e. 2-3) as it is so much faster to swap tubes than to search for and patch a hole, even if you use instant patches (but still take your patch kit!).
I'm big on cue sheets, which means I seldom need to consult a map while underway and that saves time too. Everyone has their own methods, but I adopted mine from WRC Rally (I've long been a fan) and use arrows to indicate turns and note the distances to and in between for the transit sections. It really helps me a lot and I have adopted a variation for touring internationally in unfamiliar areas. In Eastern Europe where everything was written in Cyrillics, I'd spend a few moments with my maps or GPS before bedtime or in the morning, making a cue sheet for the day. I felt it left me more time to devote to scenery and it was easy to check signs against my cue sheet to make sure I was still on track or needed to turn and if so, which way. One of my favorite randonneuring accessories is a little plastic clip with cam-action that velcros to my handlebars and securely holds my cue sheet even in stiff headwinds. Called the CueClip, it is sold here among many other places...
https://www.amazon.com/Cue-Clip-Sheet-Holder-Black/dp/B00DTVUM9Q Of course you don't need a fancy clip; you can just jot some notes on a piece of paper and tuck it in a pocket or in your HB bag map case. If you do, be sure to use waterproof ink or a pencil and Rite In The Rain paper helps, too, as it doesn't get soggy if you need to fish it out in the pouring rain. Some links...
https://www.riteintherain.com/faqs?gclid=Cj0KCQiAt66eBhCnARIsAKf3ZNGdUcg3bXVV2X2V52pePmHnup_hC8Sjaf_PSQtbWFvwLG6e9uutoKoaAqDAEALw_wcB...I like my Fisher Space Pen to write with, as it is waterproof, temperature stable and being pressurized, will even write upside-down or at an angle so you don't need to use care in storing it upright. See...
https://www.amazon.com/s?k=fisher+space+pen&gclid=Cj0KCQiAt66eBhCnARIsAKf3ZNFsepUJEABV-TbstMX5pQlITBf5C-MHS53L8U4qEU_ZWPI5u4DAVtAaAp3aEALw_wcB&hvadid=616991222582&hvdev=c&hvlocphy=9033029&hvnetw=g&hvqmt=e&hvrand=16148862108356411025&hvtargid=kwd-105309480&hydadcr=24659_13611768&tag=googhydr-20&ref=pd_sl_8hqd6t77ij_eI prefer mine with a clip so I don't lose it and the chunkier barrel sizes are easier to use with even fingerless biking gloves.
Maybe something here will be helpful, Paul. It's been fun to think about your upcoming efforts and to be asked for thoughts. I'm sure you'll do well and if you find it doesn't work this year or isn't a fun goal, no worries! There's plenty of other ways to enjoy a ride.
Best, Dan.