If it’s going to be your main router, then don’t. Unless you like getting beaten having your whole internet access go down when something goes wrong with your host or you have to reboot it. A separate, low-power consumption physical box for the router is just better, unless you have some kind of redundancy in-place (and you mentioned replacing everything with 1 system). Even an Intel NUC with an el-cheapo USB NIC (for WAN) would suffice if you don’t have Gigabit (or more) to your house (and I’ve ran such a setup for a small office with 20 people with an 100 mbps WAN connection).
Highly biased, so my answer will always be yes. I love software RAID because you can run it anywhere with no headaches like compatible RAID cards in case something goes awfully wrong (I hear the situation is not as bad as it used to be, but still, better make the switch).
Just do it!
VLANs are optional if your switch supports it (or if you have direct connection between your router and servers / *nix boxes). Visit my recent wiki (still in beta, need to implement IPv6 rules) to make a secure network for home. You don’t need lots of rules, just the default-deny on WAN from pfSense / OPNsense and blocking some additional stuff from going out of your network and just having separate networks for untrusted devices.
Add / block whatever else you feel you need based on your threat model (e.g. make a proxy and block outbound 80 and 443 connections, maybe also block port 21 and maybe email ports if you aren’t using email clients and only use web mail). I’ll probably improve on this tutorial with an optional more restrictive policy, like blocking everything and only allowing http and https outbound through the proxy. But for now, home users don’t need lots of block rules, which is why I named this “easy to follow.”
Do you really need that? I’d personally just do 1 VM for Windows and passthrough the whole card. Unless, of course, you got a higher-risk threat model and want a separate gaming VM and a video-editing VM that requires some GPU acceleration. Or, as mentioned in CraftComputing’s video, have more people play on 1 card.