I'm going to make some wet lay moulds by hand using the EG160 tooling gel, EL160 resin and 450g carbon. I wanted to bag the moulds over night while the resin cures but want to know if regulating the vacuum is necessary? Does anyone have experience of using a regulator with hand laminating?
These moulds will be used to make parts in an autoclave. Obviously, tooling prepreg is available but the original part can't really be exposed to heat or pressure.

I think it would help to vacuum bag them and that there's no reason to dial back the pump.  If you make sure you have a good bag stack and well slip jointed laminate and process material (peel ply, breather, release film) you should definitely get better compaction and less voids by bagging.  You will need a post cure to get the Tg of the resin high enough to use for prep-preg but this can usually be split between a supported postcure to whatever temp the mold will take followed by a slow ramped unsupported postcure off the tool to boost the Tg of the resin.  

You may have luck for small tools with chopped strand laminate.  I have made autoclave tools (low temp prepreg) from vinylester resin and chopped strand mat.  The key is getting good gelcoat and a perfect skin coat ply or the autoclave will punch the gelcoat into the voids in the skincoat backing ply and your parts will have little bumps on them.  Be careful that the CSM doesn't have a binder that makes it not compatible with the epoxy.  Regular light woven 200g cloth hand laminated in epoxy might be fine for small molds where CTE-mismatch isn't a big deal.  Make sure you roll it well with a bubble popper after each ply and use plenty of epoxy.

Interested to see how it comes out - good luck!