Colin, you are overthinking the process.
Let Ohme carry out the survey and take it from there.
One step at a time.
It may very well be a standard install.
Worst comes to the worst, its too expensive, or too much hassle, you can move on from there. Cancel the car and go looking at ICE.
Just say to Ohme the survey is causing you distress and anxiety and they have to do the survey. Its not far from the truth.
Leave it to the specialists.