I'm looking for some help in choosing what storage to get for my tiny home server.

I have a Lenovo ThinkCentre M73p i5-4570 with 16GB of RAM. I will be hosting Plex as well as my own cloud and a few other bits and bobs. However, I'm not sure what storage to get. I will be using the 2 USB 3.0 ports for external storage and the internal SSD for the OS.

I'm thinking about getting 2 x 2TB, but HDD or SSD I do not know. I figure I'll use one for storage and the other to backup that storage as I can't loose what's on there.

Any suggestions or things to think about when choosing my external drives would be much appreciated as I'm new to the hardware side of things.

Thanks!