Not sure about mixing a pesticide in paint. Borax/borate/boric acid is commonly used to treat unpainted surfaces against insects. I always spray it during renovation work when I have walls open. Boracare is one brand. Usually you mix it in a sprayer or dust it on exposed surface. It is a mineral relatively harmless. Same stuff that is common in roach powder, the old fashined kind that still works well in comes in giant yellow bottles. Diamataceous earth is a substitute and is the common ingredient it swimming pool filter material. A bag of filter material is dirt cheap?
None of this is a repellant though. The glass like qualities get carried back to hives or nests and the insects sort of get shredded like in a Kill Bill movie.
As for priming? If you are using paint, you must prime everything you plan to paint. If using solid stain, you do not need to prime. It is not a mythological primer and paint in one product but is self priming on wood surfaces.
And come on, you have come this far in prepping the surface. You really know the answer as to whether you should get by with one coat or put on two. Right?