I upgraded from RR's Oreo build. Before flashing I repartitioned the phone using the method described here
and the even more detailed instructions posted by douguluskaien on page 12 of that thread. The flash went very smoothly and although the phone initially ran hot it cooled back to normal after a few hours of what was probably background processing. With the 1.5G system partition I was able to install the micro version of GAPPS. I've had that experience after flashing new ROMs on other phones as well. I also discovered the bundled camera doesn't work and installed Google Camera. After starting up Google Camera, the original camera worked also. I tried connecting bluetooth headphones, and even though I could pair the headset I couldn't get the phone to send audio - it just kept playing through the phone speaker. I also found the default font size a little small, but changing it to Large in the Font Size menu got it back to what seems like normal.
I have one major issue which I realize is not directly related to the ROM. A custom version of TWRP is required to support the non-standard partitions, and that version is based on TWRP 3.2.3 and doesn't support device encryption. Does anyone know if an updated TWRP will be available that will allow me to encrypt the phone and still do recovery-related stuff?
In summary, this is impressively well along for a build that's only been live for a couple of weeks. This isn't my daily driver so I don't need absolute stability, so this is plenty for me for now. I just won't leave the house with it until I can encrypt.