Here are, for what it's worth, my two cents.
1) Explain how you choose your winners and second/third runners. I haven't been surprised by the winners in the past, but some of the second or third runners were sometimes questionnable, in my opinion, and other entries could have been chosen instead. I'm pretty sure you had good reasons, just tell what they are, none to write a novel, a few lines explaining what guided the choice (topology, textures, beauty render ??).
2) Winners may be the same people from one challenge to another, of course, very talented, but if some happy few confiscate the competition, then the outsiders won't even bother to enter the challenges. I think that, like we can see in some figurines painting challenges I entered when I was (much) younger, the winner in a given category (for example : regular 3D or print 3D) should not be allowed to enter the next competition in the same category, or they could participate for an honorific title, without being allowed to get the prizes twice in a row.
3) Portfolio : producing 10 models in one month is quite complicated unless you belong to a studio with a huge production capacity. Because, if you are a freelancer you can't allow to spare all your time producing ten models in one month especially for a challenge, with potentially low sales afterwards. My advice would be to split this category in two : best individual portfolio (let's say 3-5 models) and best studio portfolio (10 models). Of course, any producer being composed of two or more people, should have to enter this last category instead of individual portfolio. This would avoid having the portfolio categories won by studios against whom an individual can't compete, and would also avoid portfolios composed for individuals of 2-3 good models and 7-10 crappy ones.
My own experience in these challenges is that to be able to produce 10 models for one challenge, being an individual with a full-time job, I had to rush and publish unpolished models - so after two attempts, I just stopped trying because it was just not satisfying.
Again, my two cents.