I have pretty strong feelings about this, but I'll make it short.

1) A bar table is fun. It's not really pool.
2) A 4x8 is the minimum. If you can get a 9 footer, and have the space for it, go for it. Bigger is better in the pool world.
3) They take up a lot of space. That said, in the three years I had mine, I played, on average, 5 games a day over those three years. Much more than any pinball I've ever owned. If the attraction of pinball is a that it is a "real", "visceral" game, pool is that times ten. I really love pool.
4) Moving and refelting are a built in cost. Don't do it yourself. Splurge on good felt (preferably Belgian). It should likely last forever.
5) Don't buy new. You won't get your money back. Be ok with this.
6) Buy a copy of Byrne's Standard Book of Pool and Billiards. It's the bible in the pool world. I'm normally not a fan of bibles, but...
7) Play. Play often. With people better than you. You'll get better too.
8) The best thing about pool for me is seeing the shot. Not actually making it, which is glorious fun, but seeing. Seeing how to run the table, seeing how to line up shots, seeing the 1 in a 100 shot that no one else sees and calling it, and when the stakes are on the line, making it. Lovely.
9) Billiards was such a part of my growing up. A friend called it my misspent youth, but it was such a wonderful, formative time that I heartily recommend any 20 something to take six months, hang out in pool halls and just enjoy their lives. Quite a learning experience.