I have about 5-10 domains that right now I don't do with them nothing. Is it smart to build html page with links to sites?
Yes, I would also suggest to create at least some content in those domains. You might end up receiving tons of traffic from the search engines
If they are hosted in different server abd having different class c ips then yes they'll count as back links. Most search engines now count only clas c ips now a days.