Avast is a decent AV, as long as its not slowing down your system and causing issues then you should be fine with that.
The windows firewall only blocks incoming threats , not outgoing , again if Comodo is not causing issues then its up to you if you want to keep it.
As far as your router, its kind of hard to explain as it does and does not have firewall, what I mean by that is when you set up your router and created a passcode, only computers that know that passcode can access your network. If you have other computers in your home that share that router or if a friend drops by and you log them in with the passcode , any other computers outside that wont be able to access your network unless thay know that passcode.
Vista was not a very secure Operating System, if your computer came with Vista it may be to old to upgrade, if not you may want to think about upgrading to Win 7, again if your computer is pretty old , due to old hardware it may not be able to upgrade to Win 10. From Vista to Win 7 there is no free upgrade so you will have to purchase Win 7 .