Max lvl? - 80
Is there good PvP? - depends on which zone, you have 15 (decent from what i've heard), 30 (pretty popular lately), and 80 (kinda dead from what I have seen)
decent enough PvE for lvling? - PvE is pretty good, it gets slow when you get around lv 50 but thats just about any game really. Quests dont help that much on leveling, well not after about the first 10 levels.
EXP rate? - decent, gets slow sometimes sure, but the PM's give us some nice xp boosts every month (depending on the monthly schedule posted in the promotions forum for that month)
Do you absolutely have to invest in AP to build a good character? - to build a good character, no. to build an uber character, pretty much, although I know some that have made uber characters (called toons in this game btw) without buying AP even 1 time.
Are there many or any good farming areas? - yeah there are pretty good bit of farming areas, there is one that is open only at certain times (Oblivion Insula). There are also "token quests" which provide you with tokens that can be exchanged for a lapis box (which provides either a potion or random level 7 lapis) these quests are for level 60 (through 69 really but the easiest and most farmed quest is at 60) and 80, you can either sell the boxes or open them for the lapis, either way can be good money just depends how lucky you are.
How is the game play? - I love the gameplay, I play on the Alliance of Light, we have a nice community overall, a few bad apples but that is like every game. Personally, I've enjoyed Shaiya more than I did when I played WoW.
Oh, one last thing. The servers Lailah, Gaia, Etain, Teos are merged into one big server, each acting as channels. So essentially you have Original Shaiya (OS/Merged) or Shaiya Phoenix (PX)
Welcome to the community
Hope to see you in game.