i think those lags caused by a map are overestimated. nobody lags on ruins, field by the river, village... and these are some really quite big maps. (the distar tournament map we were using was huge, but i mean it really was HUUUUGE, that was the problem).
i don't think its necessary to have shitloads of arenas (nobody will ever use them), i'd rather prefer a few arenas and fine tuned with nice decorations around them and spawn, thats all.
for now we agreed on 2 same sized small arenas for very small fights (that can take place at the same time so people won't wait inbetween fights so much) and 1 arena that is already built (its size is perfect). for now i can't imagine i'd need anything else.