Running

I think you can do the distance without that (I've run 10 miles with no refreshment), but that would limit the speed you could do it in.
I aim to run a half marathon (or, at least, a half marathon distance) barefoot, this year. Really silly ambition, but achievable.
Full marathon can be - certainly much, much more physically punishing than a half marathon. Luckily, you're attempting the latter. Like I said, this is achievable simply from a decent level of fitness, without any super special training or technique.

I run 10k's without anything. for 20k's I need carbs. This partly down to being a busy father, with little time for prep. I like gels

I dont think a half marathon is a distructive distance in the way a marathon is. Like you say. But running for 2 hours requires stuff, 5 and 10k's dont.

I stand by my long slow, strength building, sunday runs.

All the best on the bare foot thing.