I think you're right on track. Any smaller DS bike has its limitation, but so do larger ones. Having a truck you can throw your bike in puts you at a huge advantage,I think it opens up way more possibilities.
Buying a popular bike has its benefits to, there are always a lot of used parts around. People will sometime strip their farkles off and sell them separately from their bike, you can then get some decent parts for way less then new. That always helps out when you starting out and you're buying everything.
I think your budget sounds about right, bike, good gear and you've got some room for upgrades.
Buy good gear, it'll probably outlast the bike you start out with... the Fly trekker is a great recommendation for a helmet, and goes to show you don't have to spend a lot of money to get worthwhile gear. Good gear doesn't cost a lot, but crap gear does.
anyway, happy hunting!