I’m a Finisher at a cabinet shop and I use MDF all the time. We get to keep scrap anything in the shop and when I say scrap I mean like 1/2 sheets of ply and mdf. When I’m finishing I have to prime first for paint....I take scrap 1/4 “ mdf and prime it with all the other stuff I’m priming. Long story short I have used it for my airbrushing and pinstriping and it works great. I sand it smooth and finish like I would with any metal primed things. I do suggest sanding the mdf first with a minimum of 320 grit. Mdf seems smooth but when you prime and paint not so much I usually sand 320 before I apply the primer, blow off dust and use your hand to feel for any dust. Hit it with primer thpaint n when dry I sand again at 320 then another coat of primer. I sometimes sand again then hit it with a pre cat lacquer...then I have a nice white surface to practice on. If it’s something you’re gonna keep forever hit th other side as well, if not the mdf will bow eventually.
HTH
Joe