Although I'm not part of the team in any way I'd suggest you take your own ideas regarding the overall terrain that is given and the layout.
I've started mapping for the SurvivalGames aswell and I felt like a 256 radius (that's 512 circular diameter) sphere was just good enough for a small map, about 350 radius is quite big and 512 radius is a very large area.
The original map has a radius of 500 from the center point, so the overall lenght is 1000 blocks. That being optimized atm for 24+ players.
I feel like the original map is "simply too big" so in case you have less water around or less flat areas, about 250-400 radius is just fine.
Obviously I dunno if Chad and the guys that are accepting and revisiting maps will accept smaller maps but I couldnt imagine why they wouldnt if they are well made.
And I'm also sure that there will be a need of various sized maps in the future so just go for it. My advice