GPS can only be used as a primary means of navigation if the equipment and installation is approved and certified and correctly indicated in the POH/AFM in accordance with EASA AMC 20-5. Otherwise it may be unsuitable for RNAV/GNSS operations.
Correct for
BRNAV, but not a lot of your students will be going IFR, FL095+ which in the UK is Class A anyway, and in virtually all cases an IR is needed
(I say "virtually" because there are a few places in the UK one could go IFR on the IMCR alone at FL095+ but one would be hard pushed to find non-Class A CAS
)
Not applicable to normal private flight, however.
So my FTO is paying a fortune for instructor liability insurance for......??
You are paying that in case one of your instructors is involved in an accident, and the student (or his estate) sues, or there is a ground damage claim. Or some spurious personal assault claim which has to be defended... a possibility when one is spending a lot of time alone in a plane with the student.
There is no known case of a comeback (in the UK) against an instructor simply for poor teaching methods.