You should be fine, The brick wall should hold some structure together.
But since you are going to put a retaining wall in for the stairs, you should tie it into the foundation with rebar.
This will require two small footings at the stair well and some concrete walls.
My opinion is the bilco concrete stairs and hatchway.
This is the Easiest, most cost effective solution.
Most of what you have posted will work however the hatchway door meets egress and is a long term no hassle solution.
Been here and done this, yada yada and the T-shirt.
Get the widest model you can, then go with the composite doors. The metal doors always rust from the inside where no one paints them and the moisture builds up. Presto-rusto.