i'd run a bead of caulk along the edges and all if you're going to do 45's. the resin will seal it, yeah, but if you have a big enough hole (which doesnt really need to be that big), the resin will possibly seep through. the 45's do little to no help with output when building the box really tho. it's been in a couple topics. one was a recent one.
spray the resin afterwards. if you paint the port, and you use plain resin, you'll be able to see the black, but it wont be as nice and glossy/solid black. it'll have a transparent lookin cover over top of it.