Post by BigH
1. You need an Item Level (ilvl) of 440 to enter Heroic dungeons and 460 to enter the first LFR (Looking For Raid). You should be close to 440 when you hit 90 if you've been PvEing.
To reach that mark easier you can buy/craft a set of PvP gear, there's an older set at 450 and a newer set at 458 (Crafted Dreadful Gladiator's Dragonhide Robes
etc). Those are pretty cheap on my AH usually. A lot of the factions have some high ilvl quest reward once you reach a higher rep level, but those usually take a while to get.
Once you hit 440 and can do Heroics, generally the fastest way to get into LFR is to grind Heroics for Valor Points, then convert those to Honor Points, and then buy the 476 Honor gear.
Also, there is a 522 Necklace (Flanker's Battletags
etc) available for VP at the Throne of Thunder Quartermaster in Townlong Steps or on the Isle of Thunder which you can buy at Neutral with the Shado-pan Assault.
Scenarios (3-person mini-dungeons) are also a way to get 463 (I think) drops, plus VP.
2. Same as above pretty much.
3. For the most part the best gear comes from raids, or Conquest Points for PvP. So you have to earn these yourself, you can't buy them. But there are a few higher ilvl items which are crafted and you can buy, though they're usually really expensive.