The little Suzuki DRZ400 is an awesome choice is you will be riding offroad most of the time. For tarmac you will prefer a larger capacity bike which will keep up with the flow of the traffic. Something akin to a YAMAHA XT600E or a YAMAHA XT660 will do that job nicely. Other budget possibles include:
A 600cc plus bike will cope happily with huge amounts of luggage as well as heavy riders.
For more technical trails the little DRZ400 is truly in a class of it's own. The DRZ is also probably THE most reliable 400 to be found (anywhere).
Pity there are'nt any decent (low milage) DR350's left..
For me the planning and anticipation is almost as enjoyable as the journey itself (but then again I'm sad like that).
Whatever you decide on, I wish you well.
Triumph Bonneville 800 (2004), Yamaha XT600E (1999), Honda XBR500 (1986).