Yeah - I'm gonna recommend the rental thing as well for gigs. Of course you'll still need something for practice, but you shouldn't need much in a practice space.
Renting versus buying for a larger (gigging) PA makes sense for a number of reasons: 1) you'd have to play a TON of shows to make buying one worthwhile (I don't imagine a place with no PA would pay the band very well), 2) no maintenance and 3) you'll get to try out different setups as you rent them and learn what really works for you and your preferences. Plus (number 4) if the band braks up, nobody is stuck with an expensive PA lying dormant in their basement.
Furthermore, yeah, where are you playing that doesn't have a PA? That's only happened to me once, and a band as bad as mine plays only the crappiest of crappiest joints!! But - even if they don't have a PA, if you're just starting out you'll likely be on a ticket with other bands, and one of those bands may have a PA or you can all go in together on a rental if need be.
To answer you other questions - brands to avoid: BEHRINGER
. Peavey PA stuff seems just as solid as all of their other stuff. You can find Yorkville PA stuff for cheap all the time, and it's decent stuff that takes a beating. As for setup, I don't know why it has to be powered mixer versus powered speakers ... I like passive speakers and passive mixer, with power amps so I can configure things any old way I please. It's all very modular that way, too. But then I've never been accused of having good ears ...