Again, I find it a good idea in making the part twice longer then cut it in half afterwards ! Neat cutting indeed is a matter of concern.
I would probably go with resin infusion, with a layer of gel coat as first layer which command me to prepare the wood surface (but I'm still afraid not to have a perfect cosmetic finish, which is the purpose, as you guessed). Maybe I should think about making a glass fiber mould from the wood part, then sanding the mould to the perfection, then proceed to resin infusion for making the final part. I also thought about finishing the part with a clear coat on top of gelcoat (once the part is demold).
The matches box was only an example. What I'm looking for is the best practrices for maknig box-shaped pieces in general. When you know how to do one, you almost know how to do any type of CF boxes
Thank you for all your precious inputs (and sorry for my rough "french" english :-p).