Fun trip; I hope you can make it happen.

A lot of research is evident, but it's always easy to nitpick. Like others, I think transport is way underfunded--especially these days. It sounds like you're bringing a liquid fuel stove, which will probably be taken from you before your first flight. I'm not sure about an airbag canister, but the same might apply. You might want to double-check your visa prices (but I'm from the US, so I know little about U.K. passports). Same with inoculations--and Malarone, if so inclined, can be a major expense. I don't know why you'd carry a solar panel on a bike which can produce more electricity than you need; likewise that 30 feet of rope, unless planning to winch stuff up cliffs every now and then.

I'd bring a pair of regular trousers and a button down (or other semi-presentable) shirt, because you spend a lot more time off the bike than on. I think you're a bit overboard on underwear and socks. I was going to quibble about the fuel tanks, but then remembered the tiny CRF capacity.

I've traveled quite a bit on a CRF 250. They'll hold 50 mph easily enough--60 if you insist (and maybe carry a change of front sprocket). That's fine if you're steering clear of multilane highways and flat, boring places, but that's easier said than done. My country, which is spectacularly scenic in parts, consists largely of flat, boring places, and the same is true of Australia, Central Asia, much of Argentina, Chile and Peru... On the other hand, slow speeds mean it's actually a lot more comfortable without the windscreen than with, so I'd leave that out.

Last, I seriously doubt you'll find reasonable transport from Jakarta to Ushuaia, and it's really difficult to bring your bike into Vietnam. It sounds like there might be some holes in your research, particularly around transporting the bike. I know you're saying you'll wait until closer to the day, but these are basic, underlying issues and unlikely to go away.

Hope that's helpful.

Mark