Mixed answer.
You can hook up as many computers as you want to the network, but you cannot connect to all of them. There is a limit as to file sharing connections, and it may affect what machines in the workgroup you get to see and connect to.
So, yes, you are limited from an operational point of view - all those machines cannot interact with each other, However, if each machine was used just to surf the internet, they could all work (10 or 20, whatever...) So, it depends on your definition of "connected together", just by wire to the same switch (unlimited), or logically to each other (limited by Microsoft)
There used to be a MS limit of 10 network connections for workgroups, which included file shares, printer shares, and RPC links. I suspect that limit is still there, in some form....
To get around that, some people set up a Linux file server, and you can then allow "many" PCs to connect to it....