+x+xI honestly would just spray a 1k primer and then use a wax based release instead of pva. This won't dissolve the 1k primer and when demoulding in worst case you ripp off the two little primer patches off of the plug, but with a little acetone they will wash right off and leave you with a good surface otherwise.
Unless the gelcoat attacks the areas of 1k primer, causing alligatoring in both. Then it's a lot of work to fix again. Fairly likely to happen.
Classiccarbon, yes use any gun you like. PVA can cause it to rust out, so make sure you clean it out well if it is a gun you want to keep in good condition.
Also yes, you can use spray glue (though I'm not sure why you want to if you are making a mould?). Just be careful if you need to reposition anything after sticking it down, as you may lift the PVA film. It is normally ok though.
Ah yes my mistake don't need glue haha. Thank you.