trees recieve morning sun and afternoon shade in summer, until they grow into the sun. I think this will work well based on mango in trees around here (and that mango trees I planted in the full inland sun require shade cloth to grow well.)
Plants are spaced 8' on center in photo, from left to right 7' tall manilla seedling, 4' tall grafted Mallika, 5' tall multi branch espada seedling. Does this seem appropriate for socal?
Soil is clay/sand and will remain so with top few inches removed from the concrete replaced with amended soil, and then several inches of mulch to bring level with driveway.
Your plan sounds good. North East side next to the house is perfect for Riverside. Even my place in Burbank is cooler, four mango seedlings I planted on the North East, 2.5' from the wall, are growing very well. One is holding fruits at 3 years old, and the others are over 5 feet tall with multiple top branches spreading which indicates they will also have flower next year. I prefer to planting mangoes on this cooler side than facing the hot sun on West, SW, or NW. I have 7 mango trees planted on the West side, one feet to 2 feet from the house wall, and they shade the wall for a cooler house during hot summer. I had to shade the trees in hot day above 95F, or the leaves, fruits, and trunks would be damaged. No damage to house or foundation at all, as mango has deep tap root as compare to citric, avocado, or Sapote which are destructive if planted near the wall.
8 feet between trees is too wide. I would prefer to have 4 feet between trees, then you will have 5 instead of just 3 trees.
I know every book and experts are talking about mango loving sun and hot ground, including the famed CRFG.org. But my 15 years experience in growing mango in SoCal, young mangoes prefer North East side of the house for protection. This is why in hot tropic places, we only see young seedlings grow in the bush and not wide open space with no protection from the hot sun.
As about the soil level, to avoid root rotted during cold winter rain, I would bring the new soil level up to the surrounding concrete top level for drainage, then add wood chips on top if you like.