The maximum number of stations you can have on your ring depends on whether you are using a retimed or a non-retimed concentrator. If you are in doubt about your concentrator, check the documentation that was supplied with it. The maximum numbers of stations are as follows:
Concentrator
Maximum number of stations on ring
Retimed
132
Non-retimed
250
You can mix copper and fiber-optic cabling in the same network. Refer the documentation supplied with your concentrator for details.