Here are your answers Pong:
1. Press V and try moving, it allows you to basically fly. Hold shift to go faster, and press V again to turn it off.
2. You cant (without many extra mods), but the answer to number 1 makes this pretty unneeded.
3. Yes, big models have trouble with stuff like that. The reason that dragon worked better was because it is an easy bug to fix, but it has to be done when it is modeled, so you couldn't fix it without changing the entire models. So yes, it happens, and no, you cant fix it.
Now about the pic, Its very good for a first, the angle was just right. However, lighting is completely absent, which can be fixed very easily by doing this:
1. Press and hold Q to go to the menu.
2. Choose the "Post Processing" tab.
Now experiment with these settings, mostly Simple DOF, Bloom, and Sunbeams, though Color Mod can be useful in adding more color to environments. I know way to many maps, so tell me if your in need of scenery. Also, I highly recommend this map, its very Zelda-ey
http://www.garrysmod.org/downloads/?a=view&id=38281
Hopefully this helped!
EDIT: Well, Price already answered these, but I still put a ton more info so it doesn't matter.