Moving from PC to Mac

Your Mac will read the data on the drives your PC used to use. Windows can't read Macintosh format, but Macs can read what your PC has written. You don't necessarily need a new drive for files.

However, if you have a new drive you could - indeed should - use that for Time Machine backups. See the Apple support document here on drives, and read also the document Back up your files with Time Machine on Mac.

Your question suggests you haven't tried to plug the drives into your Mac to see what would happen?

Your Mac can write to it too. I recall some years ago a friend at my office who was a PC user had a big external drive he needed to wipe and his PC refused to format it. It was too big for Windows to handle, he said. He gave it to me to format for Windows which I did on my Mac and returned it to him the next day. Welcome to Macintosh.

I've bought a few external drives for my family in the past year or so. The "standard" size is increasing all the time and I've found it difficult to buy a powered drive smaller than 4TB and even the hand-sized USB drives are at least 2TB.

I can't recommend one above another but there are obvious brands which dominate the market. SSD has lots of advantages over the physical/spinning drive so you're on the right track.