I fear your understanding of RTM and VARTM is wrong to begin with. RTM is neither the method you are looking for, nor the method you are thinking about. I guess you are looking for resin infusion.
Quick answers to your questions:
1) (assuming meant resin infusion) no. The foam is obviously filled with a gas, under atmospheric pressure or above. You can't collapse it by vacuum application. To be precisely: the pressure forces on your foam are the same in or outside a vacuum bag. But the bag itself can easily warp softer foam cores.
2) (resin infusion) yes. The are lots of videos available for this method. This is the standard procedure for custom board.
3) usually both sides are separate pieces, with a slight overlap around the board.
4) many variables here. It doesn't take that much. If you are using a good rigid foam, it would only take one or two layers of 200-300g/m^2 on each side. Mounting points have to be reinforced with extra layers.

Look out for resin infusion board making videos for further instructions. There is a wide range of different tutorials.

Hello everyone,
I am very new to composites, as part of my degree I am doing a composites design course. One of the assignments for the course required me to pick a composite product and reverse engineer it. I picked a surfboard with carbon fiber rails (https://www.youtube.com/watch?v=0w2SVZk3uAs). The surfboard components are:
1)    Foam core – Polystyrene core is created using a mould
2)    Glass fiber – Hand layup is used to lay the glass fiber, cured with epoxy
3)    Carbon Fiber- UD carbon tape is used for the rails

Hand lay-up is a time consuming, labour intensive method with low reproducible accuracy. I need to suggest an alternative manufacturing technique. I was wondering if RTM could be used as a suitable alternate manufacturing technique? I tried searching on it but didnt find info on RTM for surfboard manufacturing which is making me doubt if its a suitable technique. I have a few questions:

1) I presume VARTM can not be used in this case as the polystyrene core will obviously collapse under vaccuum. Can someone confirm this?
2) If I were to use RTM, could I used my foam core directly as the mould? layup glass fiber on it and then inject the resin?
3) In the case of hand lay-up, is the entire foam core (top and bottom) covered with one piece of glass fiber fabric or is each side done separately?
4) How do I determine the number of glass fiber plies need to withstand the load exerted by the surfer?

As is obvious, this is a completely new field for me so my questions might seem very dumb but I would be very grateful if anyone could help me out a little.

Thanks!