You'll need 20 Red Xichrons to get into the final levels.
If you can, save your smite rings for the very end, or at least the boss levels. The enemies in the first levels are easy enough to kill with regular weapons.
The Escape rings are useful in later levels when you go back and complete a specific aspect of a quest within a game, so you can get out of the level quickly. I've only ever used two or three of them, so I don't really ever bother with trying to collect them.
Don't have much time right now - I'll try to write more later about the weapons, but there are a whole bunch.
I'm going to have to go boot up my old PowerBook (it boots in OS9, so I can play all the old games on it) to refresh my memory about the rest of it.