Separate subsets, segregated traffic. Easy to avoid crosstalk by setting channels further apart or using 2.4ghz and 5ghz

At home I have one SSID as a main wifi, and the other is guest wifi and IoT or other random devices.

Main downside is getting it setup and maintenance.

What are the use cases? More RAM is nice but could be overkill if you’re bottlenecked by CPU, and if this is for running a few simple VMs or as storage then you may not need much of this.

RAID is generally a good thing but don’t get complacent, follow the 3-2-1 method. I.e. you might be better off saving the cash and using a backup script to push stuff you really care about to the cloud, and pay for cloud fees vice hw.