I agree about source must be included for distribution - this then helps the mapper community as well as the custom-playing community.
Also, depending on overall size, all files are combined into 1 pk3, no campaign file 
Are the maps aimed at a certain number of players? I’d assume not, but naturally they’d tend towards smaller teams.
Maybe make it that there must be at least 8 spawns per team.
They must also support LMS mode (an obvious choice given the likely nature of the maps).
Then the usual quality finishes - no missing textures, no scripting errors etc.
I’ve got a couple of clan servers, I can probably blag at least one to run potential maps for testing.
Rules should be aimed at getting decent quality final results, not discouraging.
Also, I’d have a pretty strict and relatively short deadline - often it gives people the motivation.
I’d say a month or so from the start would be reasonable given the small size of the maps here.
People can, of course, submit as many maps as they like too.