Hi PixelsnPrint
Welcome to the forum
My only knowledge of CNC construction/building has come from following the threads and reading the build logs, but if funds allow i would forget about using wood or plastics as construction material, Ally profile is an option but this can get expensive and you will find that steel box section is your cheapest route. For the sort of duty you are looking @ you could get away with round supported rail. Have a look through the build logs and you will get a better idea of the way ahead, and if possible post a sketch up detail drg and the lads will put you on the right track.
Regards
Mike