I have a 2012 2.6ghz quad mini server with 16gb RAM and original internal Apple 256gb SSD. However I boot into Sierra from an external 1TB USB 3.0 Samsung T3 SSD. This machine also has two 5TB USB 3.0 hard drives for media storage and a BlackMagic UltraStudio thunderbolt video interface for my Sony studio monitor.
I mostly work with 1080p30 in FCP, with no proxies. My work with Logic is mostly 8 tracks of live audio recordings and a handful of plug-ins. I usually record with a Zoom F8 recorder and just transfer the audio files to the Mini via the SD card, however it can also be used as an 8 channel USB audio interface.
This all works very well for me. You don't say which Mini you have though, the i7 quads are 2x to 3x faster than the base 2012 dual i5 Mini's. Sorry, have never used Abelton. If you've just started getting errors however, I wonder if the hard drive is starting to fail? OTOH, it sounds like you have more peripherals than I do.
I gave my base model 2012 Mini to the kids a few years ago, and it was also setup to boot from an external SSD, however they started getting lots of errors and crashes from the internal hard drive (that I had configured to do time machine backups of the SSD). Finally just gave up on that machine.
Anyway, here's what I get from the Samsung T3. From what I've read here in the past, this is about as fast as you can get from an external USB SSD on the 2012 Mini.
And this is my original Apple internal SSD. Definitely faster, but the only differene I really notice is that the external drive takes about 30 seconds to boot and the internal is about 15 seconds.