I currently have an SSD for boot and HDD for storage.

Save the steam save files on a separate are of the boot SSD for now, the easiest way to make steam work again is to re-download all of the games. Making a new steam library on the new drive, I did this a few months ago, I originally just transferred all of the files over but the way steam works, it was not happy, some games worked others did not, it was easier for me just to delete them all and start over. I have unlimited downloads, and a 500mb connection just set it to download all 500gbs and left for the weekend when I came back they were all done. Some of the data saves are stored in the cloud, others are not, any game that is run outside of steam like through Ubisofts loader are stored on the cloud. Other saves are in each data folder, so one you download the files its usually as simple as copying each individual save file back into it's respective folder.

Installation is really no different than any other drive, except for having to install a 2.5" to 3.5" adapter for the drive bay. Connect the SATA cable let your motherboard, and then windows find it, format and start copying.