Multiple thrones is fine. construction shot could include one or all of them, your choice. If you prefer the team prize, no worries! You'll be able to choose if you're one of the winners.
Immortal Tower and Deus Praetorium are the ones that I think should be in the top 10 for sure. I hope they will be in top 20 and get some reward! Of course I agree with m4dcow with all of those throne rooms. Over 100 entires are a lot to choose from. Can´t wait the top 20!
The construction shot presentation is up to you. The "room" can be an open area yes, it can be more an "area" than a "room" if you prefer. Yes. Of course! I guess it doesn't have to be a 360 environment, as long as it is large enough to provide good variations for the 3 presentation shots. No offline renderer (VRay,…