I make model airplanes last year i learnt a lot of carbonfibre in a company where they make real airplane parts. And now i will build my first carbon model plane. I don't have experience in making carbonfibre parts and I also don't have a vacuum table (i have tried to make it but it failed) but i have made a wooden mdf mold and i'm gonna make a plaster female mold of the male wooden mold. Then i can put the woven carbon into the plaster mold en add the epoxy resin and then I can compress these two molds together to create the effect of the vacuum.

To be honest I would personally never use a MDF mould or Plaster, its way to porous and it will probably leave a bad finish on your part or contaminate your resin...

Thanks for your information

Mdf with filler should be fine as a base for paint; i think it's good to polish the painted buck surface but don't worry too much about very fine scratches as the tooling gel coat will have a slight orange peel texture so I put my effort in to the finished mould not the buck.