I've read all your suggestions, and I agree on most percentage based stuff involving HP/SP, I did a quick testing but obviously being alone I can't really test it accurately. I think once the beta testing phase starts, I'll be able to get much more useful feedback from the users!
As for Dirty Tricks and why I am using SP each turn, is because this way the skill can be activated with less starting SP needed, and other party members could keep it active with SP regen/buff.
For example let's say Dirty Tricks I required 25 SP to start. For 5 turns x 5 SP a turn = 25. So total is 50 SP. But using this system even if the Mercenary has only 30SP he can start the skill and run for 1 turn, and if another party member gives him a SP potion that refill 50 SP, he could keep that skill active for the whole duration. In the other case, he would need to have necessarily 50SP, and maybe his current max SP available is 45 SP
Anyway, will need a lot of testing that's for sure, with Loren needed 2 months. There are less skills in this game since there are less characters, but more variety I think!