I'm trying to be completely self-sufficient in my approach to biking. That means using my legs to generate not only motion, but all the juice needed to power lights, computer, GPS, radio, cellphone, laptop or tablet, and anything else I might add down the line. I'm looking at either a Shimano DH-3N71, SON20 or SON28 hub generator, lithium-ion battery (to be determined), Dinotte XML-3 headlight and Daytime Red taillight. Ideally, I'd have everything hard-wired to draw whatever current is needed from the battery, but if I have to use the intermediate step of recharging the device batteries from the master battery (or skipping the master battery altogether and charging everything off the hub generator as needed), I'd be okay with that. If I could also use the hub generator to recharge spare batteries for the various devices and swap them out as needed, that would be okay, too, but I'd rather not have to mess with popping batteries in and out all the time, much less carrying and keeping track of the spares.
I'm not that electronically inclined. I do realize that everything needs to be the same voltage, or else I'll have to step up or step down the voltage to a particular device. I also know I don't want to overcharge the battery or batteries, either the li-ion or the device batteries, so I'd need to incorporate a meter and/or shutoff circuit. I'd envision something that would automatically kick in to charge the battery when it's low and kick out when it's fully charged, but if I have to do that manually with a toggle switch when the meter reads low or high, that's acceptable.
So what do I need to do to accomplish this? Anything I'm overlooking?