It really depends on your budget. ISS System is very flexible in terms of where to install different services. Ideally, you may want to have one server run only one service. Typically, you will run Admin/(Event) Monitoring services on one server, and Recording, (Live) Streaming and VA services on three separate servers respectively.

But if your system is 32ch max, you may run all the services: Admin, Monitoring, Recording, Streaming on one server, and VA services on another server. VA service takes a lot of CPU resources[1]. If you are installing multiple services on one PC server, such as (Live) Streaming service and Recording service on the same PC server, you need to assign different (RTP) incoming port ranges for them. Refer to Incoming port range in the glossaries.

[1]  4 core CPU can handle upto 8ch in VA service