Ok, let me address your questions. Ochita, I think Blitz will do just fine. The ninja is just very versatile. I don't want to push him towards any specific build, so I'm not going to mention anything specifically, but he definitely has options.
Harry, you are probably right. For the Arbalest, I'm going to rule that you get one free point for each tier of Bolt mastery. As in, when you reach BM 2 you get snipe OR sharpshooter, and at BM 5 you get the elemental barrage of your choice. You can buy into the others when you want. You get Heavy shot right now.
Tiruin, Errol had it just about right. The "Lv 5" next to Salve, for example means you need 5 points in Cure to unlock it. And cure needs 1 point in heal mastery. Remember that there are other options for revival. Nectars revive, and as long as you win the fight/otherwise escape with the body, you can get them revived in town for a nominal fee.
Errol, Welcome! Glad to have you. Farmers are pretty OP, you are gonna ruin the balance of my game! [/sarcasm] Horseplay is a skill that obviously had more value in the original game, because sometimes you wanted to change it to day or night, but the only way to do that was to sleep at the inn, or pace back and forth in the dungeon (obviously getting into fights). Horseplay let you pass the time without fights.
Alright, I'm going to decide players soon. Let me get out of bed and eat and stuff first >.< (Don't keep your laptop next to your bed, it promotes bad habits). If I had unlimited time and ideas I would happily run two groups simultaneously, but I'm worried it would be too much for me. If we get going and I think I can manage it, we can give it a try.
EDIT:Oh, and I found a better link for the skills for EO IV. It's in the OP. It actually has the skill trees.