Pro Sites site ID's on a Multisite With Parent and child sites using directories

I’m making a membership site network, where all user sites follow the same general idea, that operates as follows:

The main site is

The user signs up and gets a site

I’m am using Membership and Pro Sites to do this and there are a lot of unanswered questions in the installation instructions.

A big one has to do with site ID’s. Will each member’s site have its own site ID? It seems like this could get out of hand very quickly when my network becomes successful. Initially, I am only offering one Basic Level until I get a lot more adept and knowledgeable at how all of this tech stuff works. The only real variation would be how long the user signed up for as all user sites would have access to the same features. Will I be able to set it up for the parent site and have all of the child sites follow the same Pro Site configuration automatically?

I would like to set it up so I can expand it to add features later such a access to premium themes and plugins. It seems like Pro Sites would accommodate this fairly easily.

Also, there doesn’t seem to be a clear indication as to what the site ID number for each site is. How do I find this easily for each site?

Thank you,