Don't spray until the last layer. Spray uses more paint, and will make a mess. With a roller everything gets even spread on the surface.
Put regular white wood-glue (mix it 4:1 glue to water) on the saw-edges of MDF first, it will fill the porous sides to get smoother finish later.
Roll on prime, sand, repair, prime the repaired parts again, sand again, prime the repaired parts again, roll on 1 layer of final paint, sand, spray the last layer.
With high-gloss you see every glitch in the woodwork. Pick semi-gloss unless you are an absolute master in the woodwork and wood repair.
About the paint. Here in Europe I have good experience with Sigma S2U Satin. It is an alkyd paint with high scratch resistance. They also pre-colour the prime for better coverage. It is important to leave the cab alone for 2 days after each prime session and a whole week for each final lacquer session. Then the paint is fully hardened out and sanding goes way better. And leave it another week until you move it around the house. Bad for your patience, but worth it. Hang some wet clothes around the paint-area and paint the last layer (near) naked (unless you are the monkeytype, than some good sweaty nylon clothing will do) for best dust free performance.