The problem with a big gas tank is that it is bulky and heavy, and most of the time you don't need it. (You want to get off the bike and stretch / drink some water every few hours anyway.) For the relatively few times over your trip when gas stations will be far apart, you can always buy a plastic gas can and strap it to your bike for that stretch - or, if there's no other option, just use a regular large drink bottle, etc.

Do you mean to use that tech while actually riding, so it will need to be charged up continuously? Have you calculated your expected total power draw?

You could certainly upgrade the charging system, but one option would be to have a big power bank constantly charging off the bike, and your tech charging off the power bank. E.g. I have a Telwin Drive 13000 unit that can actually be used to jump-start my car (and certainly my bike), and it's lost maybe a quarter of a charge after sitting on a shelf for six months and then jumping the car four or five times. And it's beefy enough to power a laptop. Think about having something like that to power your tech in a camp - you're protected against draining your bike's primary battery.

Yup, LSL for example makes adjustable rearset kits and bar risers. I ran an adjustable rearset on one of my old bikes (a crappy Chinese one) - in reality once you set the bike up comfortably, you're unlikely to want to change it often. Especially on something like a T700 that already has high, wide bars.

If you want to play with carbon fibre, that's cool but carbon fibre is brittle. If you fall over - and you will, on bad roads - you can hit a rock and shatter the entire pannier. Have a look at these, for example: About – TARK - rigid but impact-absorbing.

Interesting. What information do you want to output onto a HUD? Do you actually want it on your helmet, or up high on the bike's instrument cluster?

That's a very good approach.