Some questions:
I am trying to host multiple web site on linux server.
1. Do I need to create service file to each site? Would not it cause high memory load? Why does it need "service" ?
2. Must I set different port for each web site like 5001, 5002 and if yes, how to change this port with no_source files?

Well, it's a question rather for System Administrator that hosts your stores.

Services are used to start GrandNode after every reboot of the machine, or to restart it automatically.

I know what services are for but why do I need to create it? Also how about the port change with no source version.