1) takes 3-5 weeks, depending on ur win.losses

2) depending on blizzard's arena season, note this: blizzard may or may not include new arena gears, or arena sets after a new season, it depends on the PVE progression

3) 5v5, because 5v5 you get full points for the team, 3v3 80% and 2v2 60%.
easier to win? no such thing, they all the same. what i listed was how much ur point gain ratios are.

and imo, dont arena (or rated arena) until ur prepare to face up some lots of frustration, especially being an arena scrub(ill admit, i am one as well because i only got 40ish resi and 8.2k hp, so long ur resilience is under 200 and have less than 10k health, ur a scrub and within top arena teams, ur nothing.)

your rating will sit stagnant at a specific point because the moment you get past that point, you'll be pitted against tougher team and you'll just drop back lower. bottom line, arenas are basically a whole new world of pvp, so different, they are treating it professionally with sponsored teams like you see on war3/cs/starcraft professional tournaments.

priest being holy or druid being restore is actually a good asset for top tier pvp teams, no matter what, a healer is needed and you cant expect them to heal in shadow/feral.

the only difference is that they will be speccing pvp holy or just straight disc, and pvp restore and maybe mix with balance and/or feral for survivability

no matter how attractive the rewards from the arena rewards can get, it'll only be good in pvp. pve loots come from pve, pvp loots come from pvp. certainly, there are some exceptions, such as the gladiator weapons in majority (though not all of them) but in the end those said items still spent their item distribution points on stam and resilience, in which a pve weapon of the same item level would get much higher pve stats such as agi/ap/crit/hit for example in rogue gears.

unless of course, you're just interested in getting more purples, then a mix of glad + kara having 2 source of purple income is definately the way to go. as many posted before mentioned, no matter how sucky ur team can go, just do the 10 games, if ur team doing good or in the mood, go more, if not just do 10 for the week and be done with it. regardless, no matter how low the points you can get, its better than no points. (regret for not doing the arenas the moment i hit 70, was too occupied in pve and obsessed on my rogue set/weapons)

if you wanna get a little serious, there are few gears that you can get from pve to pvp, get them, and be prepared to spend ~100-150 gold per week to spec back and forth from arena spec and raiding spec (if ur a raider or hardcore heroic person)

aka me... lol

and if ur gonna sit out in ur arena team, you need to participate at least 30% of the games to even get points.

so the 30% is just to "qualify" and you get the same ammount of points?