You could start by defnining the purpose of the bike you want, as you've been doing, and make the component decisions on hand of that. By way of example:
Do you want to travel fast or be comfortable? If you choose speed, you might choose drop bars. If you choose comfort, you may want to sit more upright and use well-cranked bars, or even city (North Road) bars, and you will absolutely insist on forks wide enough to use balloon tyres (47mm and up) with space left over for mudguards. A fast, lightweight narrow-tyred bike ("a light tourer") might have derailleurs. A low maintenance bike, fast enough but more adaptable all round, would have hub gears; many of us swear by the outstanding 14-speed German hub gearbox made by Rohloff.
Suppose you choose comfort and a Rohloff. To start with, given your age and present condition, and the fact that you intend credit card touring, 38x16 gears will let you pedal relatively easily but not necessarily quickly up most hills you will meet though you must resign yourself to freewheeling down the steepest hills as you run out of gears at the top; 38x17 would be lower (i.e. slower) to get you up steeper hills still, but probably unnecessary. Depending on precisely what you mean by unfit, 42x17 gears may be within your reach. It is better to undergear and get up the hills than to overgear and have your holiday ruined when you discover you don't have the legs and the lungs consistently to pull that high a gear train. Many Thorns have 17 tooth sprockets, and the cheapest sprocket, supplied free with new Rohloff boxes, is 16T, so a good choice that leaves your options open is 38x17, or the standard 38x16 favoured by many owners; if you find this combination too slow, a new chainring is cheap to buy and you can sell a barely used one on here, or just give it away. This also leaves you with the option of using a Hebie Chainglider to cover the transmission, which reduces maintenance tremendously.
Let's take another example, the saddle, a very, very important interface with your bike. If you want to go fast, you'll have a certain forward posture on the bike, and will use a narrow saddle, because that is what works with the posture. You may be used to a narrow saddle from past cycling, but there are alternatives that come with different cycling outlooks. A more upright, semi-sporting or comfort, stance on the bike requires a wider saddle, and the sprung Brooks have their fans, for good reasons, including that you can be hours in the saddle between wineries in France, without feeling too much pain.
Do you see how in a proper bicyclist's decision tree the choices cascade from deciding what you want the bike to do, rather than shopping for a bike that someone else has though up and put together with components he bought as a job lot on price?
Forget the technicalities; you can bone up on them later, or have your new mates on the forum give you a quick primer. Instead think hard about what you want the bike to do for you, and how best to share that with us, and someone here will have had the same expectation, and be able to advise you on the best frame type and size, and components and their scaling, to meet your expectations exactly.
It works; it's not rocket science; it just takes patience. Buying this class of bike is not a process that can be hurried.
