On 2, Make an ugly frontend, I learned a straightforward way to work with services and various kinds of backend code without front ends: add a simple web server endpoint to expose whatever properties, settings, or behaviors are of interest.
This is almost trivial if your chosen language has capabilities built-in, as in `python -mSimpleHTTPServer`. Add endpoints to return in plain text or maybe json. One thing I often do is log to an in-memory array of strings, then add an endpoint `/log` that returns the contents of the array. I usually go a bit farther and use a circular buffer, so the in-memory log doesn't grow too big.
Postman is a good tool also, though the learning curve can be a bit steep.