I have found after a lot of testing that for me, the best process was to put the first coat of resin on as thin as possible using a squeegee. After an overnight cure I sand it with 220 till it's smooth, but try not to sand through, then put on a second coat. The second coat of resin barely takes anything and adds very little weight, but does a great job of filling the weave. Then sand that after it's cured and prime. I did a bunch of test panels a few years ago, and found that 2 coats of resin is lighter than one if you want to fill all the weave since it takes less primer. Primer can be heavy.
The spray can primer will work, but a 2 part catalyzed product is better in the long run, but if you don't have a choice you use what you can get.