Where to store Logic Pro Project files

I've read through this conversation about the recommendation to store the Pro library and sound files on an external drive, and I appreciate that input. However, I do have a related question: Where is the best/recommended place to store your Logic project files? Internally or to another external hard drive (or even the one you're using for the libraries and sound files)? (Of course, I would also be archiving these project files to another external location as well.) Anyway, all that said, if I do use an external hard drive to store project files what should the minimum size of the hard drive be? (I'm using a new iMac 24" desktop and am therefore able to connect to any hard drive using Thunderbolt. That should be faster than the USB-C. Then again, the question now becomes: HDD or SSD, the latter being faster.

A lot of questions, I know, therefore thanks in advance!