Dedicated wifi for automation allows me to have devices such as Xiaomi Vaccuum, or security camera not phoning home. OpenWRT with good firewall rules completely isolate my "public" containers/VMs from my lan.
Server was built over time, disk by disk. I'm now aiming to buy only 12TB drives, but I got to sacrifice the first two as parity...
I just love the simplicity of snapraid / mergerfs. Even if I were to loose 3 disks (my setup allows me the loss of 2 disks), I'd only loose data that's on these disks, not the whole array. I lost one drive once, recovery went well and was relatively easy.
I try to keep things separated and I may be running a bit too many containers/vms, but well, I got resources to spare :)
I would never use an ISPs router for my home network. It just causes so many issues that you can easily avoid by either using your own router directly or if that is not possible putting the device into "bridge" mode and using your own router behind it.
What are some of the issues?
The devices the ISPs send out are usually the cheapest hardware imaginable and therefore introduce substantial unnecessary latency.
Where I live some ISPs also used to use tools that genereted wifi passwords based on the devices MAC address. While this is apparently fixed now, a lot of non tech savvy users still use these old devices that are basically open to anyone now.
To save even more money, they sometimes deliberately send out faulty devices (as in devices that drop connection frequently, restart for no reason, etc) which is just horrible.
I know these issues because I worked in that field and there are a lot more unfortunately...