What should I do once I've purchased a second hard drive for my Hackintosh?

I'm running out of space on my Hackintosh and I've purchased an additional SSD to install into my machine. The goal is not to replace my current SSD but for this new drive to be an extension to the SSD my OS is currently installed on.

I know that I have to install and reformat the new drive to APFS (I'm using High Sierra); however, other than that, I'm not sure what else I should do. Is there any other steps I should be aware of? Are there any gotchas I should be aware of?

Also, after I install this new drive, will macOS automatically start installing new applications and downloading files to this new SSD once my first SSD is filled?