Yes, I advise avoiding a 2012 unit altogether, ditto for the 2014 units. There's no way I'd buy an 2012 i5, and I'd avoid Catalina at all costs on a 2012 Mini. I replaunits in my company with 2018 units, my personal unit has been bulletproof, still running Mojave - it'll be sold in the next few months. Regarding Apple's macOS support? 6-18 months for the 2012, long gone for hardware. For Boot Camp, Intel has supported the iGPU in the Mini much better than Apple over the years - the drivers from Intel for the iGPU were updated just a few months ago.

Parallels is focused on Metal right now, the 2012 will be cut off in a year or two from improvements in Metal. Regarding Windows? Parallels - just don't. More money spent on a 2012 unit that could go toward buying a 2018 unit. You'd need to max out the RAM just to get decent video performance - the RAM resources are shared with the iGPU. You'll be reading for a bit, grab a beer first. The 2012 unit review were littered with complaints about failed components, bolstered by Apple employees offering that there were plenty of 'backroom' parts in this EOLed Mac - google for yourself along the lines of this and 'Mac mini slow drive'. No, the 2012 units are not worth it - this coming from an owner of one on my desk. The 2012's mobile CPU is a dog when compared to the desktop CPUs in the 2018. I respect your budget, I wouldn't buy my Mini at your budget when I know I could find a newer i3 unit that performs much better. Owner of a 2012 i7 Mini Server here, 16GB RAM with a Samsung 850 PRO installed as the main drive.

Mac mini late 2012 i7 price