Personally I never use anything lighter than 225CSM, yes the old textbooks say to use surfacing tissue, I just find there are no positives at all, except maybe on models.
I get all my fibreglass supplies from East Coast Fibreglass. For the mould I would use no more than a 225 against the gelcoat and nothing more than 2 more layers of 225 or 300. If you really feel the need, an extra strip about 100 mm wide round the edge will stiffen the wotsit out of it.
For your cut outs the surface doesn't need to be great as you are cutting them anyway, I have used layers of masking tape to cover some in the past as al I was doing was stopping the laminate from dropping into the holes.
I have never had any fisheye with proper release wax, nor PVA. I did once when I got caught out and used car polish.
I reckon the time fairing a buck/plug is no more than what you would do to fair a piece pulled off the buck and then fair the glass, and you can make the actual moulding as light as you want having seen how stiff your mould is. To me a mould is usually worth the effort. Some say "tomatoes, I say tomatos "