If you're hosting the server yourself, the only limitations are those
of the machine on which you are running the server. If you're
concerned about cpu and bandwidth limitations, then you should
probably be hosting the game on your own server.
The gamegardens.com server is just a fun place for casual hobbyists to
host games, it's not a place where someone would host a serious game
that expects to get a lot of player traffic, or use a lot of CPU and
network resources.
Presently, the only hard limits are 64MB of heap and throttles in
incoming and outgoing message rates (10 messages per second). So we
rely on game authors not doing substantial CPU grinding in their
games.
What did you have in mind?