you'll want to take the bumpers off the car to paint them. sand do all the big pre on the car, then take it off to do the sides and edges.
use a tall saw horse to hold it and do it in a place that you can leave it sit over night.
i did fix a large crack on the lower part of the front, ran out of epoxy but its under the car and not seen. its still holding today. some kits have a mesh to lay in the filler over the crack on the back side then coat the mesh to make a stronger bond, i just laid it on a bit thick on the back side and filled the face, sanded smooth. yours would need a heat gun and lots of mesh, or hot staples to hold the crack together.
your rear bumper, it may just be easier to find a used one, if not in your color, you know you can paint it.
