I think this one needs a longer preparation. Last nation cup there were only 8 participating countries, I think 16 would be nicer and possible. People from all kinds of nationalities need to be informed way before, so they can search and inform other people from their country.
The maximum amount of players on the roster should be quite much, it would be a good experience for all players, even if they only get to train.
It would also be nice if each country could pick 1 map for the mappool. The refs can always add more maps if they think its nessecary. The countries must be well informed that they should be picking 3v3 suitable maps though.

Thats all for now.