I have to say that I agree with your choice of white primer. Most of the used figs on Ebay or in any LGS I have seen are primed black and nothing has progressed past that. Black primer is the worst thing for a rookie painter or anyone who likes to save their eyesight. I truly believe that this habit kills alot of people's interest in painting. These R models have such incredible depth and character that is hard to discern under black primer. I like using white gesso mixed with a little black just to darken the shadows on the figs. Eventually I will try an airbrush with gesso so I could prime faster and more complete.
I find it very hard to recognize some of the details with black primer. I tried it once but it was a pain in the ass for me to be sure what's supposed to be cloth or limb sometimes, so I stuck with white. It also happened more than once that I recognized some details just when the mini was primed... The double-goblin from Cadwallon, for example, I never really realized before that there was one sitting on top of the other...
I didn't know about the risk with high humidity and varnish spray when I sprayed my Acherons... The result was a kind of frosty, grey veil, almost looking like dust that was on the models, covering the details, blurred the paint, it was really disgusting. I tried to lessen the hoar effect on the models by using gloss varnish, because some told me it worked and I also found this advice on some websites, but for me it didn't work that well, it was, if at all, very little. So I stumbled across another tip, but I could hardly believe this could work: a wash with olive oil. I don't know why, but this really worked! After the oil was dry (some rest I still had to dab away) I used gloss varnish. So I just have to redo 5 instead of 18, what a release.
I start with a black prime and then do a 90° prime of white (Zenith priming) to give the miniature natural light and dark areas. As for the humidity I switched a few years ago to only priming with an airbrush and have not had one fuzzy miniature since.
I started priming white then switched to black for a long time. Recently I've started using grey and I quite like that. Black was great for me - I never really had any problems and white worked well too. Grey seems the best though so far. It shows details nicely and is a compromise on coverage of following coats between white and black.
I'm a convert to grey primer as well. Black was too dark to see details and to get bright colors. White was too light to get dark colors and to really get good shading, but grey is working quite well for me.
Those are A LOT of miniatures awaiting for paint, enough to last for a lifetime.
Yeah, and that's not even half of it, there are still five tool boxes (I store my miniatures in those big boxes) from the other factions. All together, there are still about ~700 miniatures to paint. That's what I call a retirement plan...