Hi, Is it using wcf or plain sockets? my suggestion is to use http instead of tcp, this will go around firewall.
From the list you mentioned, I don't have enough experience only with Oracle, but I don't think that is a problem, because I have a experience with sybase and mssql.
Are you looking for full time worker? generally I work with free schedule, 20 hours a week, let me know if this is ok for you..
Regards,
Arsen