Some Help

[crackerjake]

This is my first time making a map, and I'm in need of some help. First of all, sorry about it being so dirty and messy, I tried cleaning it up as much as I could while damaging it as little as I could.

Now, I've got some questions:
1) What are the effects of a mountain range on an area?
2) What is the minimum size of a forest?
3) Would people take boats upriver for trade and such?
4) What kind of things would having this many rivers in one area do?
5) How long would it take for a desert to form if a mountain range was spontaneously created?

I'll also take any advice offered, of course, since I'm kinda having the mapper's equivalent of a writer's block. I'm kind of struggling on where/if I should put more forests or another lake or pond.

If it helps, here's an extremely quick and brief version of the backstory of my land:

The Diernese arrived on the shores of what is know the Dierdan Kingdom, and made an alliance with the local (good aligned, by nature) orcs for the sake of survival. The resident humans didn't take too kindly to the Dierdans being there, attacked, and ultimately failed in the face of the Orc/Dierdan forces, and mostly because a wizard, backed by a cabal of other wizards, raised what he wanted to be a stone wall, but was instead a mountain range. The effort killed him, but the attackers were soon cut off and the Dierdans and the Orcs survived. Things went on, the Dierdans and the Orcs became closer, building a kingdom together. On the other side of the mountains, a desert had formed and the Desert Men (finally, a name!!) attacked again. They formed a group of elite wizards who blew a freaking hole in the mountain range, and they attacked, and lost, again. A highly talented wizard erected a gate (dunno of what) where the hole was and named it after himself.

Oh, and the Unforgiving Isle has pirates. The Genneve Isles are where monks train.


Like I said before, this is still veeeeeery early in the development, but I'm pretty stuck. Where the star is is supposed to be the Kingdom Capital (no name yet). This is for my DnD group, and it'll be my first time DMing :p, so I'm trying to make this as good as I can.

So, can I be helped? Or is it still too early to tell?