Helge - there's no reason to pay for an SSD drive for recording - rotational drives have the throughput to easily do 40 tracks 2 48K. I'd also second OWC as they have multiple bus-powered USB-C drives; I replaced my aging Firewire Glyph drives with a G-TECH 4TB USB-C drive that's externally powered. Better to have power for one less thing to go wrong on recording. Once SSD prices come down, I'll look at them, but I've had zero problems with multitrack recording or playback, either from my new MacBook Pro or from my 2013 MBP using USB 3.0.
Regardless of what you get, I'd recommend subscribing to Backblaze.com - for one price per month it backs up your Mac and any and all drives you have, attached or not (yes you have to attach them if you want them backed up at some point, it's not wizardry). I had my old 4TB Western Digital drive die on me, and Backblaze shipped me a transfer disk in a few days. Copied the files to the new drive, and sent it back - zero cost.
If you sign up with my link, you get a month free, I get a month free. Or don't use the link - I'm fine either way as it's a great service, especially for having a cloud backup of all your drives.
https://secure.backblaze.com/r/01a5ln