You have 2 years to plan, so no worries!
China and SEA are generally pretty cheap, especially if you're coming from the UK, you'll get a mad exchange rate.
You should probably get a better idea of what you want to see/do and what level of luxury you want to allow yourself food, activity and accomodation-wise. I know I traveled Vietnam/Cambodia for about US 20/day for everything including transport, and Borneo for about US 25 a day (not including diving, but stuff like mountain climbing guides, jungle tours and white-water rafting).
I don't know how much accomodation costs in China, because that was all paid for in my case but for meals I could get breakfast off the street for US 0.25-0.50, lunch for US 1, and maybe splurge a little more on dinner.