I am running 11 servers and as a rule of thumb, I bump all the port +1 for each additional server. Here are my server launcher batch files as an example..
start .\Binaries\win64\kfserver1 kf-bioticslab?adminpassword=xxxx -Port=7787 -QueryPort=27015 -WebAdminPort=8080
start .\Binaries\win64\kfserver2 kf-bioticslab?adminpassword=xxxx -Port=7788 -QueryPort=27016 -WebAdminPort=8081
..etc..etc