Stacking shields on Kleese turns mortars into a powerful attack regardless so yes skill damage and shields are ideal
That’s how it works
I’m pretty sure the game calculates per use, not on unlock. You should be fine. If you’re not, there’s a problem
I use both and regen to make it easier to live without needing a healer or a supply station
Kleese guide abridged.
Make rifts, hold down alt fire.