Always the more the better, it depends on your OS. The new ones consume more RAM.
So that would be the free RAM when starting the game.

Yes, we plan to do that in later releases. Not worth making a low-res release as textures don't affect performance that much, except if you have a really old video card with less memory than I mentioned.
Although we will probably make an high-res textures pack.

Then I hope you're a girl...