In reply to drink_more_tea:
Hi there, I've been meaning to respond on this but haven't had much time. I've done shorter length trips but also used to plan and sell these kinds of trips as an agent. I'm not saying that makes me know it all, but the pointers I normally suggest are -
- there's a lot of world out there. Grab a big wall map and some stickers and go nuts. Both pick out where you MUST go and where you'd like to include if you can. Dont' do bags of research here, just let your imagination go. You can easily spend 12 months in once place you like or can find 3 days is too long in another, so getting an idea of where you actually want to go can help narrow down the route. If you find for example neither of you are interested in North America this can help the next stage.
- Familiarise youreselves with the main Round The World or multi continent airline fares that are available. It's been some years since I was an expert, but the big two are BA One World (using the One World Alliance carriers) and the Star Alliance one. There's also another which is a very good deal but rather restrictive called The Great Escapade which is Virgin, Air Newzealand and Singapore Airlines (while restrictive it may do exactly what you're looking at). While you can do add on sectors either by flying or going overland, the biggest single cost is that round the world fare. Don't worry they allow changes as they're built for this kind of trip.
Now based on the prices (there's a few different mileage options on some) you can decide which one is most likely to fit your needs (is it worth adding on £1500 to your far so you can see Rio for a few days if all the other places are in Asia and and the US? etc).
Don't worry about exact matches, as I said you can add on short haul sectors often quite cheap.
- Now build up a rough route. You can change the route after buying even, but now it will just allow you to start to work out the possibilities and options and tricks. For example Bangkok to Singapore is really cheap on Bangkok air (which is a lovely airline to fly with too and certainly used to have a free exclusive lounge in a number of airports) but could knock off 900 miles which allow you to complete your route without going up to the next bracket and so saving money. Also you'll start finding routes overland potentially that you would like to do and those you wouldn't. The train from Bangkok through Laos to Vietnam is quite popular and you'll see a lot along the way. Perth to Sydney by car is often considered but it's a lot of desert to see and covers 3000+ km.)
This is a starting point. There are so many options and so much to do and it's not worth trying to explain it all here, but once you start playing with the above you'll be on the way to a plan.
so one more point on planning. Don't plan too much!
Don't set it stone, don't have tight schedules, don't try and fill up the whole time. You are going to find somewhere where you decide to stay longer, you are going to find somewhere you can't stand and want to leave early, you may run in to people you get on with and put a leg in somewhere you'd not thought of to do together, you may decide you can't do X and Y so you split up and do one each as you prefer and meet up at Z. It's all changeable within reason and you're going to learn a lot about travelling once you get underway. Get a loose plan that has some leeway on budget and time and then go explore.
As for budget, this is a tough one. I'd say don't camp - as above have said carrying all that gear is going to be hellish. Either pick up cheap gear on one leg you know you'll get use for it and flog it at the end, or just take sleeping bags and a kettle and that's it (for example) for the odd rough camp. Do stay in hostels - not only are they often very cheap, they're where you are most like tomeet lots of amazing people. Do sometimes splash out, but know where and when to do it. A cheap motel in the US might cost you £50 for the night, but a 5* hotel in Kuala Lumper cost you £20, and the 5* hotel will wash your clothes and have a bath which you'll be very thankful for!
'Roughing it' can mean many things so an actual figure is hard to point to, but you can both live pretty well in most of the world for £1000 between you for a month, and shave quite a bit off if you're clever and don't mind missing luxuries. In Far East/South America/Africa in most places you could feasibly cut that in half. But with your budget I'd say thnk of it as £1000 a month to start and see how you get on. You do have quite a lot more than many people travel on.
Oh another thing, are you planning to work at all? If so then you'll need less anyway, but if you're going to hard plan anyhting I'd say it' where you're going to work and get some arranged (especially work visas , but if possible a place to) before you go. You can always change but at least then you have one firm fall back and it's less scary.