Ok here are my thoughts, I wasn't going to get into this originally and hey maybe I still won't, but I'll run the contest if you guys need someone to do board stuff and moderate etc.
OK here goes:
I think there should still be the main categories of stock tanks. If you guys want a custom tank category then thats easy to do, set a limit on price or just do glass only.
IMO nano tanks are less than 20gallons, thats just me.
I also think that 6 months is a good timeline. I mean really, are you guys just wanting to set these up and then take them down? Lets face it, anyone who knows what they're doing (or even not knows what they're doing) can throw a bunch of livestock into a newly setup tank, take a photo and then tear it down. Whats the point of that? I thought it was points for creativity and design as well as keeping stuff alive? Personally, I think the big challenge is keeping stuff going in a small water volume (anyone seen my caulerpa factory lately, its a freaking challenge, let me tell you).
Budgets, well I dunno, this seemed to be a contentious issue last time. I would find it much more challenging to come up with a neat theme/design on a limited budget rather than go whole hog and have scads of money to throw into this thing. I guess a larger budget than last time but not overly? Perhaps a set budget for equipment and one for livestock and not have them interchangeable?
Ok those are my thoughts. Feel free to tell me to get lost if you like. Remember I wield the ban stick though

(just kidding of course!)