I have 225 VIT, so around 19k hp, pretty nice for solo, and 125 CRT, it adds 52.5% base spell burst rate (without counting spell burst rate on equipment). This is the build i'm using, I really like it. Int for MATK and MDEF, DEX for decreased skill delay and casting speed. caporal also says that he's going to focus his Apostalia on increasing his VIT. This build focuses in both having a higher chance of using Spell Burst and attain much HP.
Int for MATK and MDEF, DEX for decreased skill delay and casting speed, and AGI for evasion and attack speed. *Note* - MATK will only increase if a staff/rod is being used. Magic amplifiers will increase your MATK and it's a drop from Snowman - (Kilmly Highlands). The AGI stat will be helpful only for those who wants to rely on magic amplifiers (sloted).
INT for MATK and MDEF, DEX for decreased skill delay and casting speed, CRT for improved trigger rate. The skill is CRT dependent, the higher your CRT stat is, the higher probability of it activating. This build will not be efficient until you get a skill called Spell Burst at lvl 180. You can pretty much say that you become a strong attacking tank. This build is beneficent for those who wants to be able to solo bosses. INT for MATK and MDEF, DEX for decreased skill delay and casting speed, and VIT is for the Melee DEF.