large but thin transparent resin cast in open mould

I need to make an 110 x 40 x 0,4 cm water clear resin cast. Would you recommend polyester resin for this ? The mould I will use is made of rtv silicone.

I will cast in an open mould.

Any suggestions on how I can keep the surface of my cast tack free ?

I read that cellophane film can be used to cover the surface of the cast and protect it from air. If this is correct: Do I need to place the cellophane film DIRECTLY on the surface after I have poured the resin ? Or will it do if I place the cellophane 1 cm over the surface ? (My mould is in a wooden frame, and it would be a lot easier to place (tape) the cellophane ON the frame, rather than IN the frame.)

If I need to place the cellophane film directly on the surface: When do I do that? Immediately or when the resin has started to cure?

I also read about MW wax. If that would be a better idea for protecting the surface: how do I apply the wax ? Do I mix it with the resin, or do i pour it over the resin as a final layer ?

I need a clear and transparent cast without any cloudiness or discolouration.

Thank you