PrinceMark is correct on this; Divine Might only adds +1 level to your next X number of skills now. You only really need it at like 5 or something.
And yes, Heal recovers 5% of the target’s HP per tile, on top of a fixed amount that scales with INT (this is mostly irrelevant for your build, though). At Level 10, the percentage recovery alone across the number of heal tiles is enough to sustain you (and a party) through most of the game’s content. You only need Level 10 Heal though; 15 is nice but the extra 5 tiles is not enough of a reason to give up an entire rank for over something that provides more utility or synergy with your build.