I don't have any specific boat in mind at the moment. I do know so far that I want at least two mains, two jibs, a motor and a place to sleep. That's as specific as my requirements are at the moment.
You have to help us out here. When you say 2 mains, do you mean 2 masts or 2 separate main sails for 1 mast?
A place to sleep is good, but I assume you need to cook, have refrigeration to keep food and a place to go to the bathroom. Do you want to be able to stand up in the boat or can you live in a stooped position? Tell us the amenities you need.
Most of us have one main sail that can be reefed (shortened) when wind is high and again, most of us have 1 jib on roller furling that again, can be shortened when wind is high.
Motor - inboard (diesel or gas) or outboard? Again, on narrow winding rivers, you're going to be doing a lot more motoring than sailing. I suggest an inboard diesel.
When do you plan to make this trip and how much time are you going to give it?
One other thing to keep in mind. Going down river is no problem. You can do that on a raft as the current will carry you. Going back up river is going to be the problem. You're going to need a decent engine that can fight the current.