Interesting possibilities, Dan.
First we should establish that you don't want a front motor with too much torque in the hands of innocents, or customers with road rash induced by careless use of that power will skyrocket.
The mid-motor is anyway the future for a lot of other reasons, and then the question becomes whether gears are required at all in the back of the bike, because it's a doddle giving an electric motor as many faux "gears" as its power spread will support, the limit being ridicule from experienced cyclists rather than mechanics or electrics. For flat utility riding, I don't see that a gearbox or derailleurs are necessary even at 250W. Which is why I say the gearbox above will do very well with its seven gears.
But if they're fitted separately, the question about the gears at the back becomes, and urgently, How strong are the gears. That is the sole reason for keeping my Rohloff on an electrified bike with oodles of torque, that I live among serious hills, and that I know for a fact that my mid-motor will swallow a Shimano Nexus box whole, burp, and demand another. After all, unassisted I trashed two Premium 8sp Shimano boxes in under 5000 miles the pair, and not because I was trying or because I'm careless of my property; they just weren't up to a mashing retired rugby forward.
I've written elsewhere on the forum that if the motor/battery combo is correctly chosen, three to five relatively widely spaced gears on/in the rear hub should suffice for almost any terrain, given as always that they are intelligently chosen, and that some thought is given to how the power programs of the motor will be used to fill in.
Paul, you should determine first of all which sort of indicator the bar graph is. On some ebikes it is actually what it is often mistaken for, an indicator of power remaining, a battery level, on others it gives a measure of the instant power draw (the empty bars) and the power available for instantaneous call (the bars still lit). You can tell which is which by fully charging the battery and the riding up a short steep section of road or even a ramp onto a particularly steep sidewalk and watching the bars: on the battery level gauge the level will fall slowly, recovering a little between big draws. On the instantaneous current draw meter the gauge will fall quite fast and the minute you come on the level again recover fully because the battery is still capable of delivering a big chunk of current for a few seconds. Or, if you've ridden fifty kilometers with serious battery use and the bars are still hovering up high and recovering fast, that's an instantaneous power available meter. The Chinese instructions are not always clear on which is which, and someone told me the German instructions are not well translated. You might think of the second version as a reverse rev counter, as is fitted to the modern Rolls Royce and called a "Power Meter". I've written a few brief notes about it on the forum here -- search for Coulomb Meter, which is what I've unilaterally named the second type of bar graph.
In use I have a Coulomb meter in front of me (it comes on the C965 controller supplied with my BBS-01 Bafang motor), with zero instructions, of course, and the battery level is indicated on the battery box itself, but irrelevantly so as I wouldn't dream of leaving home without a full battery, and all my rides are planned to bring the battery back home half full; my batteries last many years, and I still have the one from my first motor kit in perfect nick as a backup. If the C965 has a battery level as well as a instantaneous battery draw (Coulomb) meter, I haven't yet found the way to switch it on.
Mo' Coulombs is better Coulombs
The way to ensure that you always have enough Coulombs for the brief excessive current draw that will otherwise age your battery (actually batteries, as those boxes are built with flashlight-like cells) prematurely, is to buy the biggest battery you can afford. I'm not aware -- but then I don't keep up as I have every intention that my next electric bike will also be specified and built by me because I've already given the time and effort to educate myself -- of any commercial ebike manufacturer who gives you an adequate battery in their common models, though most will sell you a bigger, always proprietary and pricey, battery for their jam; some of these bigger batteries I also consider inadequate.
For a motor 250 to 350W ridden by a cyclist who needs intermittent assistance, not an electric motorbiker, I consider that at present 14-16Ah is a good cost/distance balance because batteries weigh a lot. Someone who expects a day's work out of an ebike better keep two such batteries on the charger overnight, and keep the spare in an accessible place, because double the amp-hours on the bike would be too heavy. Under such a solicitous regime, the life of even a well-used battery won't be infinite, but should be quite a few years. There's an alternative, of course: resign yourself to buying a new battery every year or perhaps two, and just run it down every day, like you would empty a car's petrol tank. You'll know when the time comes to replace it, or switch to the scheme above, when towards the end of every day you are pedaling along an extra 14-25 pounds of dead battery.
Three more more things while I'm banging on about it. The batteries that go into those black boxes aren't all of the same quality. The best, the last time I looked into it, were Panasonic and Samsung. The next important thing is that, unless you have serious electronic and soldering skills, don't even think about rebuilding your own battery box: you could be building a bomb instead of a battery. I have considerable electronics experience in designing and building c2000V ultrafi and haven't for as much as one second considered building my own battery box. Finally, the current "standard" in ebikes is 36V operation; the next standard is likely to be 48V, and soon the price of 48V batteries will fall as they become much more common. 48V battery boxes are heavier by one-third than 36V but give you more Coulombs while doing less damage to the batteries, more normal power, and more range. Something to consider.
