It might seem kind of lame, but since we have very limited Power Points, how would I go about making the best Defensive build? I find myself drinking tons of Blood Packs in some missions, and they're too expensive to have to buy more every day.

I was thinking to just get the very first skill, which is the AoE spin thing (can't remember the name, not in-game atm), and then pumping points into the Passives that grant +Defense and +HP. Yes? No? I don't know.

Kind of related question; The skill tree in this actually looks like a tree. Do I have to get skills in order or can I wait until a higher level and save my Power Points to skip skills?