What do you mean be "isolating" exactly ? Why don't you want Windows to "see" the LAN ? Do you have a specific worry or is it just a MS scare ?
I use Windows professionally, and have Slackware as an hybrid native/vm guest, and I don't take any particular care about "paranoid security", I don't even have any antivirus system: they slow down too much my compile time (I compile HUGE projects). I just take care of my internet usage and what I install on my computer.
As far as there's a "gateway" and my Linux machines have selected services and open port, I might be "crazy" but I don't feel any risk. Moreover I also count on being "partly anonymous", I'm not famous with a direct open machine on the internet, I doubt being targeted as an individual.
Beside I still have some tools to check malware and virus check on demand, only when I have some suspect software, which happens once in a... decade ?
But if I can give you a hint for your question, not being sure if it answer your concern, you might want to setup some kind of VPN.
Edit: in fact when I say I'm not paranoid it's not totally true, I really don't trust antivirus corporations
Edit2: sorry, if it was blurry, I don't tell you there's no risk and that you shouldn't care, my question is "naive", in that I'm curious if you're thinking about a particular risk that I'd be blind to