Wait until later today, after the Apple event - they might announce a new ARM Mac mini which would work well for you - either the older computer becomes cheaper or you get a faster Mac (or a nice iMac comes out). Since you're using Logic, it's an Apple app so it'll run well on their hardware.
The current Mac mini runs 8th gen Intel processors and only received a change in March this year with doubled base storage. It's by far the most neglected Mac. The most up to date desktop is only the 27" iMac (the 21.5 wasn't updated - there might be a 23" on the horizon for next year), which is quite a good computer for the money, just depends whether you want/need a 5k display. If you need a bit more power but are on a tight budget (and don't mind a massive boi), try looking at cheap Mac Pros on eBay. The 4,1 and 5,1 are pretty cheap and can come with some powerful Xeons. The 6,1 (trashcan) is also quite cheap atm as the GPUs are quite dated, but if you're only looking for CPU, you can pick one up with a 6 core E5 for quite cheap used. It has the benefits of small form factor, easily upgradeable RAM (with 4 slots) and even the potential for an upgraded CPU. Plus once it's finished its life, it looks pretty as an art piece (or trashcan!)
Depending on your model of 2017 MBP, I don't think you'll see that much of an upgrade going to the Mac mini, especially if you have the 15" and are going to the i3 Mac mini - I'd definitely go for like a 27" iMac or an older Mac Pro. I'd also keep an eye on the Apple Refurb store.