Much appreciated, Tom. I think I'm good now.
The issue was that I followed the instructions at https://github.com/espressif/esp-iot-so ... rationmake for my Windows v3.3 tool chain. I kept getting build errors, on both options listed. In some cases it couldn't find my other include to wifi_provisioning/manager.h. The other way, there were build errors for components I didn't need to use.
So I just copied the i2c and hts221 components to my project components dir and it worked perfectly.
What I don't know is if the esp-iot-solution is just for samples (to be borrowed from in one's own project), or if it becomes your new esp-idf. The latter didn't work for me, but as I'm still pretty new to this perhaps it was something I have set up wrong.
I've read through the sample code and provided components well enough to understand (at least for the most part) how it works, so I was successful in bringing it into my own project.