svchost firewall

Thats a hard question to answer.  Really, yes you should allow access as many legitimate processes use svchost.  But if you suspect the process as being malicious you should investigate.  Many virus will try to mimic this file so if it is running from somewhere other than where it should be, this could be dodgy.  

Have a look in msconfig, startup and services.  If there is a malicious version of this file, you will probably find where it is launching from in here.

Also, in task manager, you can right click each running svchost and click "go to service" to see what is using it.