Have you considered to buy an Arduino with some ESP32 sensors or other cheap hardware (shelly plugs / mqtt supported sockets / sensors) and just build the UMH stack on a VM or old laptop? you can skip hardware checks and all. That's what I did at home before going deep into customer projects. I have about 10 smart 'sockets' at my home office publishing to the UMH (HiveMQ) broker and created historian, dashboards and so forth!