1. lv.50.

2. There's essentially a 100% xp boost from monster kills, so dungeon roulettes are an extremely fast way to level pre-50. You will essentially need 1 or 2 dungeons per level. You can also do story quests and side quests as you go. FATEs aren't a bad way to go either, but North Thanalan is probably a little empty atm, so the xp from chain bonuses won't really work. If you can get a full party of 8 or even 6, go for it.

3. It depends how much bonus xp you get from the challenge log, dailies, and rested. Assuming you're playing nonstop though, I'd estimate 7 hours. This was prior to the 50% xp boost for pre-50 and the challenge logs though, so it should be much faster for you.