Custom maps servers doesn't work in this game. 99% people would rather play dustbowl and goldrush all over again instead of spending 5 minutes downloading map.
Mappacks will be provided.
I used to co-run a SpA custom map server with Spikespiegel. We only put the best of the best maps on it, had a complicated player-number sensitive map-cycle that would revert to normal maps if there were too few players and I made map packs with friggin' custom installers detecting TF2 install dirs and whatnot for minimum user-side effort.
Basically the moment we got bored of idling for like 2 hours straight until someone joined (and it wasn't the "passive" kind of idling either) the server died... All the SpA points I've earned were practically from trying to fill the Custom Map Server.