Hi rapier jockey, and welcome to the show from someone who's just about the same - past WC experience that keeps coming back after years of absence...
For the questions: I quite liked the planetary missions in WC3 - they're a change of scenery and give a nice sense of diving into a universe that's more than dogfights and the insides of carriers. But don't expect any radical difference - I didn't notice any gravitational pull or aerodynamics while planetside, you can even do dead stops in midair and just hang there. Well, I just pretended that it's part of the fighter's engine technology and got on with it...
To get a *legal copy* of KS might be difficult - you'll still find it on eBay, but the prices are outrageous every time (well, I'm just jealous - I had it right before me in a bargain bin in '98 and let it pass; stupid). But it's definitely worth hunting for, even in the not-so-good condition I got mine in.
For your last comment: You'll find a lot of stuff linked within the CIC, especially the WC cartoon series, and links to fan projects who've done amazing things. But for everything else, e.g. copyrighted material that may be *available* somewhere in the net, this is not the place to ask for - the board rules express a very distinct position about that.. :-]
So, happy trails,
/CM out