Definitely, I'm talking about isolating it from any insecure devices INSIDE your LAN as well. More and more the threats are coming from compromised IOT devices that essentially become abandoned after manufacture.
Unraid is working towards being more secure from threats in general, and that is going to come at the price of requiring better hardware, as better encryption and 2FA become available.
Sounds like you are in a good place with this, I just wanted to keep your expectations low with your current setup.
Honestly, if that 10 year old hard drive is well treated, I'm betting it will outlast the SSD. I've retired a good number of disks that were still working but the power to run them wasn't worth the storage they add. Old hard drives are really bad at watt per GB equations, especially when you can get a single drive that holds 18TB.
At some point you have to accept that the ongoing power draw is a greater evil than scrapping still useful kit. Run it as long as you can, then buy as much as you can possibly afford so you can use it as long as possible again. Buy once, cry once, or something like that.