Tbh, if the internet is only used on the DAW to connect to sites you completely trust such as Sonar etc then it's incredibly unlikely you will ever have any issues IMO, especially with an Ethernet connection. Wifi can cause issues.
I've never had a DAW computer that isn't connected to the internet as I believe it's a major PITA for the reasons you stated above. 15 years, no problems.
If however you are partial to a bit of 'Busty Nora' then you probably would be better having a 'puter dedicated to that. ;-)