Cool, always wanted to play with a mini, but one never came my way (yet?).
That sucks, quite frankly, and why I (many of us?) have a love / hate relationships with Apple.
Moving up one OS rank should not break things, but that's the nature (at times) of the Mac World.
I'd say that unless you have a truly compelling reason to run Mojave (I've found none for myself & actually find Mo-heavy to be, umm, clunky & heavy / slower with older hardware), then I'd say just stay with High Sierra and be happy for it.
Heck, I'm still on Mavericks for my main, heavy lifting audio machine hard drive & love the (relative) stability. I've got both Logic Pro 9 & Logic Pro X living & running peacefully together on the one drive / OS!