SSD would not be for throughput but to minimize IOPS to the pool if desired, and minimize latency. Not really needed for home use though I agree.
If you have a big pfSense box that is unused then use that. If you needed that box in the first place you should probably build a dedicated squid cache box to be able to keep up.
For home use or small company a small router box or VM would most likely not have the RAM to use squid, but your FN box would.
The use would most likely be to add a cache *for free* as you already have the hardware that is idle for most of the time anyway. Maybe an extra stick of RAM but that is still cheaper than building a dedicated box.
Last time I tried squid was with untangle. I had to stop using it as it broke some sites, content didn't update and so on. Might be better now. But unless a plugin is made it would be too much work to get running for me.