1) No you don't have to if you keep it simple, but if you really want to make more then basicgames you will have to, no pain no gain.
2) There are many, what fits you is usually the best.
3) A simple one to start with is ZZT.
http://en.wikipedia.org/wiki/ZZT
4) Yes and no, try to push it beyond what it was meant for and you get some probs (as with all progs).
5)
a. Bring new elements whilst the game progress, start basic, not too much, unlock all kinds of interesting stuffies whilst the game advances. That's called a game learning curve.
b. Look@Doom (the first one). Start with a basic map, not too hard enemies in that, let the player discover allmost all he needs to know in it. Make it harder and harder whilst he progress in your game. Adding new enemies, weaps, goodies and traps must be spread over the game. Must have enough ammo, but again not too much, better a bit too sparse than in abundance. How heavier and effective the weap, how sparser the ammo for it. Don't exaggerate the secret areas.
Don't forget multiplay, certainly implement LAN also.
Golden rule for all those who want to create games:
Don't make it too easy, too easy is boring in gaming. Don't make it too hard, too hard is frustrating.
This is the must difficult equilibrium excercise you will have to accomplish, not too easy, not too hard.
Join a forum of gamemakers.(Plenty of them).