booting from an external drive..... or, rather, not.....

hey Apple Fam,

Got an issue I have not been able to resolve myself even with KBase....

Just purchased a mac mini m2, base model, and a couple of glaring issues for me right off the bat, hopefully one of you Experts out there can guide my hand with:

1. i QUICKLY reached the storage limit when installing my music production software and library. before i was even halfway through the bare bones essentials b eing downloaded. Seemed odd to me so i looked - 160gb of storage is being occupied by "Other USers" - and i am teh only user of this mini. It's actaully rather disappointing, the salesperson i spoke with ASSURED me that this was the machine i needed - said "8 gigs of unified ram is more tahn enough to handle music or video production along with the m2 processor". Thanks, man, for convincing me to flush $600 down the drain. this leads me to number
2. i knew 256gb wasnt gioing to be enough, so i bought one if usbc hubs that has a NVME and a SATA slot inside to ghold more storage memory - and a 2TB SAmsung 980 pro NVME SSD M.2, and i had a SATA SSD with 1tb on it. I was going to just route installations to the 2tb and keeo the SATA SSD for storage ovewrflow, and only run macOS and system apps from the internal ssd.

This was proving to fail also, as when i went to run the apps i noticed all of the load was still on my internal ssd, defeating the purpose of moviong it all over to the external drive.

So i went to l format the drive, install macos and just use the 2tb drive as my startup drive. I went throujgh all the necessary steps, and it finallylet me choose the external in order to restart and run from that drive.

but when i choose it and hit reset, i now get an error message sayind SDError 108, says its having trouble setting up this drive as the startup disk. i have tried it in both APFS and MACOS extended.

I've checked disk permissions,reinstalled and re-reisntalled macos, cried in the corner, wrote it desperate love letters, had a fling with a windows computer to make it jealous, I am out of ideas... i even thought about resorting to gaslighting and dark psychology, but I'm trying to change...

any and all ideas, big or small are welcome...... and needed.....

thanks in advance...