New Players Tips and Problems

[Zephiroth]

I just started this game and never played the others. I never play games on default difficulty, always one step higher. Hard mode. I've been playing my warrior class Viking, but may have messed him up, I wanted him to be good physical damager, but I put some points into his magic for some options. Is that safe at higher difficuties? Should I be focusing on Melee or Might tree intead of the others, like the Magic tree? I don't wanna start over with him, got about 7 hours in. Should I start over, can I make it through the game in one piece?