SSD sizes for Premiere Pro setup

Depends on your project sizes of course. Hardware guru Bill Gehrke's tests resulted in the discovery that everything on one m2 nvme was fast enough. So if you can use one of those, you don't have to worry too much. I use two of those. Project and all files on one, and boot to one also, with PP setup and using all the default locations (c: drive) for scratch disks, previews, etc. I can peg my cpu and graphics card when making proxies and the disks barely register. 

Disk 0 and 1 (c: and v:) are nvme's

I do a lot of editing on a 2018 Macbook Pro. It has a 1TB internal SSD. I use a 500GB Samsung T3 SSD for my Premiere Pro cache files. And I keep my footage and project files on a couple of different SSD drives depending on the client and project. Currently, I have my personal work on a 1TB Samsung T5 SSD and I'm working on a client project using a SanDisk Extreme Portable 2TB SSD.

My OS SSD is 512 GB.

My media SSD is 1 TB.  (I don't do 4K).

Mt scratch/export SSD is 512 GB.

I only load media for work in progress on the media drive.

I'm running a series of SSDs, some only 500GB, a couple 1TB, one 2TB, and have no troubles. These days, I'd guess staying with 1TB or bigger just to have enough room to do something without always having to move files on/off the drive.

Neil