redoing foundation parge

hi there, coming to you from southern ontario canada. just have a few questions. i removed most of old flaking parging, and thinking about redoing it but i have many questions :

1. some of the mortar between the blocks are crumbling/loose, and there are some cavities, should i use mortar (type s or n?), spray foam , parging, or caulk to fill these holes?
2. should i buy parging mix or make my own? (2 bags of mason sand + portland cement or mortar?)
3. is it even necessary to parge? any alternatives? dont want it flaking off again soon.. my climate is similar to mid-west usa..(detroit area)
4. i believe water was getting in behind the parging from water dripping down from bricks and then in behind parging.. should the parging be flush with the bricks then? the parging that was on was only like half an inch thick at most.
5. attached is a picture of window. the parging was super brittle and came off there, now it looks bare. wondering if. i should spray from around the frame of the window then just reparge or can i use mortar or concrete instead? looks like it will need a few inches of parging or whatever to create a downslope on the base, and even the sides are like a few inches deep, theyll need to be filled somehow as well..


anything i should know please let me know.

pictures :