Okay, as for your Stat Build,
I find Str=Agi>Int is best.
From lvls 1 ~ 10 pump about 10 Int for now, then put the rest into Str.
11~20, starting putting more Int like 25, and then starting putting 2/3 of the pts into Str and 1/3 into Agi.
21~30 Leave your Int at around 30 or so, then once again, put it into Str and Agi, refer to the stats points guide Sambo made so you can get your stat bonuses, too.
From there on out, jsut continue just Str and Agi, enough power to do above-decent dmg and fast enough to hit it before it hits you, plus if it does get to you, you have higher Evasion now~
As for Gunner or Striker... honestly, I'm not sure myself, all I can say that Striker is cheaper and have easier-to-get weapons. Gunner on the other hand, I heard it's quite pro but I haven't much experience in it.
Hope this helps. D: