Looking at the rules of the campaign that you are already running, you covered almost every complain that I have when look at many other campaigns (no minimum quota, no forcing to write in certain boards etc) but one thing that I think would improve your next campaign is to open it for lower rank members too, more specifically Member and Full Member ranks.

I know that there are no many quality new members that are climbing up those lower ranks, but I am sure that there would be at least few good ones that you could get on board. You don't have to set up a specific quota on how many of those can join, but it wouldn't hurt to keep it open for them, just in case some hidden gem appears. Tbh, I am surprised that more campaigns are not allowing lower ranks, seeing how hard is to fill campaigns with quality high rank members.