Should I move my home folder to my HDD to reduce writing to the SSD? I recently added an external SSD to my 2012 Mac mini, connected with a USB 3.0 cable.
I also have a 500 GB HDD and everything works fine.

I am just wondering if it's recommend to move the home folder to the HDD to reduce the writing to the SSD.

One more thing, since the addition of the SSD, I'm avoiding entering sleep mode (again, to prevent pointless writing to the SSD) and I'm turning the computer off instead.
Is there a solution for this?
To disable hibernation go to terminal and type 

sudo pmset -a hibernatemode 0


If you'd like to reenable later down the line use:

sudo pmset -a hibernatemode 3


As far as moving the home folder, I feel is a bit silly given the price of ssds. If you do want to do it that's fine, but I don't think most people would suggest doing so. Especially given that it's an external drive connected with a cable I would suggest leaving everything on one drive. Less chance of things going wrong, just make sure you have back ups.