internet security - Is my network infrastructure visible outside of my wireless router?

I have a wireless router which connects to the Internet. Do external sites and services know that I'm using a router and it is not a final PC?

For that matter can external services (and perhaps my ISP) find out that I may be using several devices (computers, mobile phones, virtual machines or whatever) to connect to the Internet and not just one? Can they find out the details of the final devices? Like host names, models or whatever?

If so how can I prevent disclosing that information?