I have two filemaker server instances, one with 5 seats for a small team to directly access, and another with 40 seats for a larger team to access. The database on the 40-seat server uses the smaller server as an ESS data source to pull information, when needed. This is working fine; however, when a client connects to the 40-seat server and data is accessed from the server with 5 seats, FileMaker uses one seat per server. This completely goes against my needs for separating services by teams, and then sharing relevant data between locations. I have paid for 45 seats overall, and with just 45 users it appears I will run out of seats. Will I need to increase this to 45 seats per server to prevent workflow interruption?
You can't setup another FMS as ESS. ESS supports only limited SQL ODBC servers. So on your setting users access to both server as FM client, as you saw.