Grab yourself a Mac mini Core i5-8500B (Late 2018):
https://everymac.com/systems/apple/mac_mini/specs/mac-mini-c...It's an hexa-core 8th-generation Intel Coffee Lake processor with 65W TDP, has USB-C / Thunderbolt 3, as well as upgradeable DDR4-2666 SO-DIMM memory modules. It's also one of the last Macs to support dual-boot via Boot Camp, which will provide you a nice sanity check if you need to go deeper into performance profiling (i.e., Windows 10 vs latest macOS).
Also - make sure you have an Apple Developer account, as you will want to be able to appropriately package the application, including signing.
This machine will last a while.