The maps are not built to cope with more that 8 players per team, so your largest team size would have to be 8, rather than 9. My own server can only cope with 8 players total, so I would suggest setting the small team size as 4 so you can use mine in case Cozworld is unavailable..
The defensive maps always have one particular race defending if the team plying defenders specialises in that race they get an unfair advantage. I would suggest sticking to the tug of war type maps like digsite, orbital, lycantium and ichar IV.
You had better contact CoZmicShredder directly about using his server(s), he might give you admin right or maybe even setup a dedicated server.
How about steam Gifts/Vouchers as prizes?
Beta 7.25 will be out by the end of this weekend i'd like you to use that
