1. Max level is 20, you get 5 att points from 2-10, 10 points from 11-15 and 15 from 16-20. There are two additional quests giving 15 points each, totalling at 200 attribute points.
2. There are several different versions of PvP, but I don't do any of em. Let someone else answer that.
3. In Factions there are two sides (thus the name), but you don't really choose since you can swap sides as often as you wish. You can choose to fight for one of the sides there, but it doesn't have any long-lasting effects on the game except for (eventually) giving you a title for your fighting effort. But still, in short, no.
4. They all start in the same place, but it does of course depend which chapter you choose to start in. Prophecies characters will start in Tyria, Factions characters in Cantha and Nightfall in Elona.
Just a tip, check out
GuildWiki. It can answer mostly anything related to direct GW facts.