1) One of the basic ideas of the Spanish is to put pressure on e5, so that white can provoke the favourable trade exd4 cxd4, building a strong mobile center. For more ideas, you may need to do some research, buy a good book, or take some lessons. If you have a specific question on a specefic move, please ask 
2) Against 1.d4, the simplest is to install a pawn in the center : 1...d5 and try to maintain it there. KID is okay, but more difficult to learn.
3) There's no hard rule here : if you have some interest for an opening scheme, then try to learn and play it : the passion and interest helps building the knowledge. However, it's perfectly okay to stick with the Spanish for some time, as it's a very instructive opening anyway.
Earlier on I asked this forum what I should learn while playing white. I got a variety of answers ranging from playing variations of e4, to playing just the Spanish to playing d4 somtimes.
I weighed all the arguments and learning just the Spanish seemed to make most sense to me. It HAS helped me learn a lot. I'm not looking to revisit the question entirely. I'm sticking primarly to the Spanih.
So I have a couple of questions:
1) Can the advocates of "beginners should play only Spanish if possible" guide me a little about how to learn more variations of it? Where can I find the lines? Beyond the opening book on this website and chess365. I want to learn *why* certian moves are being played.
2) When playing black, and my opponent does not play the Spanish, what should I attempt to do? Particularly when my opponent plays d4. What are good openings for black as a beginner? Someone once told me to try the Kings Indian...is that a good one for a novice?
3) Can the advocates of "beginners should play only Spanish if possible" guide me a little about when its a good idea to bring in another opening? When do I know I'm ready? I want to learn smart, so I dont want to do anything prematurely, but I dont want to wait longer than nessesary either.