SOAP is certainly verbose but I think you would find the advantages of using HTTP addressing greatly outweigh the extra parsing time.
For example by sticking to HTTP over port 80 you get past firewalls easily. The server support for HTTP (for example
Tomcat) is well developed. It seems to me that coordination for 10 players using anything other than a client-server-backend model would be quite tricky.
A big decision to be made is how data is formatted - can you express the data required as serialized Java objects?
The web service design of SOAP & WSDL are really aimed at ease of public access with generalized clients - since you are building your own client, you dont need that.
Bill