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 :)
WIth my previous ISP, I swapped the ISP's router with my OpenWRT's and everything worked fine. With my current ISP, it appears that it's not that simple to swap the router altogether. But I'll be honest, the biggest factors are price and number of routers/switch. As I want 2.5gbps, I'd need a router with at least dual 2.5gbps ports. The WIFI6 offering is also quite nice. And if I can't swap my ISP router, it would just add another device. In a perfect world, I'd have a single router running openwrt, with wifi6 and couple of 2.5+gbps ports (but unfortunately openwrt doesn't play nice with most wifi6 routers and these routers can get very expensive) For now, my ISP router does the job and I haven't had any issue (yet)
You could spend a little for a prosumer router and AP. I have a very similar setup with a cable modem, edge router X (ubnt), a single UniFi AP, and a service running on my server (this could be replaced with a separate hardware device or Raspberry Pi, but the server is going to be running anyway). It's been rock solid since I set it up, compared to the WiFi/router combo with open-wrt I was running before that struggled and needed restarting regularly.