I am not up on the latest models of hardware available. Some general ideas to consider would be a large screen. (24" minimum for a desktop and even as an extension off a laptop). The interface icons can be difficult to make out on the 13" Retina screens. You don’t need the super powerful CPU until you are rendering large projects. But still get an i7 as it will benefit you with other graphics software you are likely to utilize being an artist. The graphics card is more important. Look at the minimum spec requirements of Harmony to get an idea of what your computer should have. I’d try to get something at least as much as the fastest recommended GPU if your budget is large enough. 16GB RAM is enough for now.
Apple didn’t offer anything appealing that fit this niche so I built a hackintosh. If it failed to work I had the option to use Windows. That is the only reason I would use Windows but once in Harmony the software is identical with the few conventions specific to the OS. The Mac Mini does not offer a good enough GPU and you cannot install enough RAM. Same really applies to the regular iMacs. Of course the iMac Pro is adequate but the basic configuration begins at 5 grand and you have to get the most RAM you will ever need when you initially purchase the system because it is soldered in and cannot be upgraded later. So that is a huge initial investment. The garbage cans are off target, over-priced and overkill for Harmony. Helps make a Windows unit a viable option.