Today was the first day for priming parts. I've decided to use a light single coat of Rustoleum's self-etching metal primer for all of these parts, based on its convenience and recommendation by others. This primer also has the benefit that it dries in only 10 minutes, so it's very quick to get back to work.
After priming the spar, ribs, nose ribs, and flap hinge brackets, I started using my hand squeezer to set the first rivets on the assemblies used on the right flap. I also got some practice drilling out bad rivets after seeing a handful of them were incorrectly set crooked, smiley, or with a gap. However, I was able to successfully remove and re-squeeze those few rivets without any drama or damage to the pieces. Then I clecoed the parts all back to the spar.
What's next? I have to finish assembling the hardware parts on the flap hinge brackets and then set the special "double-flush" rivets tomorrow. Then I'll probably rivet what I can to the spar.