The three things to worry about with drives here are speed, capacity and reliability.
1. Speed is important for transferring quickly if you want to use the
CineSSD again soon, if you need to copy the footage quickly for other reasons, and for editing high bitrate footage.
If you never need to dump footage fast and you don't mind using lower bitrate proxies for editing, you can work around having a fast drive.
If you do get one, I'd probably edit there and then move things to larger, slower, cheaper drives for storage later on.
2. You'll generally find that larger drives are slower or significantly more expensive. Large, slow drives are fine for archiving, but not ideal for editing and terrible for quickly copying the contents of the
CineSSD as I mentioned.
You will probably end up buying more HDs than you expect too because you can fill up half a TB shooting 5.2K RAW in as little as 15 minutes. ProRes is a lot smaller, but you could still potentially fill a multi-TB drive in a day if you aren't careful to conserve space.
If you are careful and you remove shots that don't come out right, etc. you can get several projects on a drive, but when you add up the initial footage, the proxy files and renders made by your editing software, etc. it comes out to be a lot of space and ultimately more drives than you'd expect if you keep your original footage after editing.
If you can only get one drive now, I'd decide whether you need more space or more speed right now and buy accordingly.
3. Hard drives fail eventually. The first month or two of use is actually a time when they're more prone to failure, but even if a drive's been working for years, eventually it will stop. That means that you should, when you can, set up a system to duplicate everything you shoot that you don't want to risk losing.
Preferably keep the backups in a different physical location, online, whatever you prefer as long as you can't lose everything in one place.
So far I don't have any Thunderbolt drives, so I can't give advice there other than to look up speed measurements and comparisons (and reliability) in reviews if the drives you're considering.
I'm actually dumping to and editing on consumer level USB 3 Seagate drives...it's not ideal, but with some patience and workarounds it can be okay. If I have to shoot something where I will need to quickly dump the
CineSSD and get going again though I'll have to get faster drives and/or more CineSSDs.