1) Your funds are going to vary depending on your drops, if you merchant, etc. It's really difficult to establish an ideal number there.
2) Yes, you should.
3) You could consider getting 6 booster after you've gotten around 10 haste or something, but that's a matter of personal opinion.
4) After maxing critical and haste with 6 points in booster, you should max drain. After that, get booster to 18 (you won't have enough points to max it, but this way it will still have the same duration as shadow partner) and max mastery.
In the end you'll end up with:
Critical - MAX
Haste - MAX
Booster - 18
Endure - 3
Drain - MAX
Mastery - MAX
For training, try Ludibrium: Terrace Hall around your late 20's early 30's (Brown Teddies). Around your 30's you might wanna try chronos, and in your late 40's, 50's try jr. yetis. Sorry, I'm not too much help in this area, perhaps someone else can give you a more definitive outlook.