I wonder if a second opinion might be a good idea? Or talking to a clinician with a background in genetics or genetic oncology, or to a genetic counsellor, as Kate suggests. It is true that whether or not you get a gene test doesn't change your condition, but the results would affect the recommended care pathway, and could mean you avoid having unnecessary tests.
There are other conditions that cause fibrofolliculomas, which are associated with different symptoms. e.g. Familial multiple discoid fibroma - there is no cancer or lung symptoms associated with this syndrome, just fibrofolliculomas. Seeing as your kidney scans are clear and you haven't had a lung scan, it could be that you have this rather than BHD. Without a genetic test, it is impossible to tell.
There have been two reported cases of patients with Birt-Hogg-Dube also having lipomas. From just two cases, it is not possible to conclusively say that the BHD caused these lipomas, and it may simply be coincidence.
I highly recommend that you speak to a healthcare professional with a background in genetics and talk with them about whether or not to get a gene test. The only way to conclusively diagnose BHD is by finding a mutation in the FLCN gene. It is true that sometimes genetic tests are incorrect leading to a false negative result. However, sequencing is done multiple times, inconclusive results are repeated and sequencing technology is so good now that the chances of this are exceedingly small.
If the results come back negative, it is most likely that this is because you do not have BHD and can therefore avoid having unnecessary lung and kidney scans. If the results come back positive, then a screening regime can be set up for you in line with the current quidelines. The only life-threatening aspect of BHD is the kidney cancer, but as the tumours are very benign in their behaviour, if caught early (with a properly drawn up screening plan) then they are unlikely to pose a significant health risk.
With many thanks and best wishes,
The BHD Foundation/Myrovlytis Trust