If using epoxy one thing to consider is yellowing.....some epoxy resins are much better then others in that regard. West resins for example at least used to be very yellow, as are others. Wouldn't worry about vacumn bagging a small part. The main thing is getting the excess resin out of the lay up.
To answer your question you could use the oem hugger coated with mold release and do your lay up over that. Do one lay up check and if it is good let it harden for awhile but before it goes completely hard start the next layup so you get a good bond. I would not try to do the whole thing at once if you haven't done lay ups before, rather build it in several layers. This will give you time, and experience. Use a good pliable squeegee to lay up and remove excess resin. It is easier to trim things before the resin goes completely off or gets too hard. Get a good scissors, and lot's of acetone to clean the scissors and squeegee, and anything else you want to clean resin off of. Cut the tops off gallon jugs to make acetone baths, use two or three so the last stage acetone is clean and won't leave any crud on you or your tools. Use a good respirator and gloves and an apron and bad shoes and clothes. After you have your layup done you can remove it from the mold.
you can then sand edges, drill, etc, lightly sand the piece for a good bond and do the gloss coat with a brush. You can then wet sand and buff. If you burn through just add another gloss coat to the area. You could prolly spray the gloss too and even spray poly over the epoxy but the bond may not work so well that way. You could also spray the epoxy with a gun. You will prolly have to thin the expoxy though. Dunno it that helps, there are other ways, this is just the way I was taught. Clark Foam may still carry everthing you would need also. They supply the surf board industry.
If you use poly instead of epoxy, the resin process is a little different between the lay up and sanding coat. the lay up resin remains tacky, to continue lay ups. Also you will have less time before the resin goes off, unless something has changed, it's been ten years since I have worked with the stuff. But poly will be clear, and makes finishing easier also or finding a poly in spray can for finish work or later touch ups easier.