" One quick question: in my training, I've been taught to say call sign and flight level/altitude (or passing level) on first contact with ATC but I noticed you tended just to give the call sign. Probably sounding pedantic but is there any reason for that? "
Once you are in CAS in the European IFR system, they have you on radar and can see your altitude, or the cleared altitude if you are climbing or descending. If they want a confirmation they will ask for it. There is no harm in giving them the level also, and on an IR test you really must do what your instructor told you the examiner expects.
But there are degrees... UK ATC are top notch, but in some places they struggle, especially with really marginal ELP (english language proficiency) so one needs to use belt and braces there, and sometimes I will give them the level and even the next 1 or 2 waypoints.
"I note that the pressure was reducing throughout your flight. Didn't note the QNH on departure 1019/1020?
Based than on about a 4mb drop along the route assuming 1013/29.92" was set in the CRZ."
It is usual for the GPS altitude (which is what the subtitle shows; that is the true altitude AMSL) to vary over a flight, due to pressure and temperature variations, even if flying at the same FL. No idea what CRZ is.
"You filed FL100 when FL090 would have been appropriate for the direction of flight."
In Europe, almost nobody cares because it is a radar controlled environment. Also there is almost no traffic at the lower levels FL100-200. There is virtually no GA. A few regionals fly in the high teens. Very occassionally ATC say they want you at FL100 or FL120 but not FL110 or some such; I recall this from Belgium.
"Perhaps when you call the French controller for the first time you could try "Lille N***** with you squawking **** level FL 90"..."
Lille should have had me on the handover from London Control, so they know about me. This isn't like a handover to London
Info which is basically a dump
It is also not like UK Class G "IFR" which is VFR in all but name and you generally need to give your squawk from changing from say Farnborough to Southend etc.
"You checked GPS altitude against the pressure altimeter, this means Vertical Nav is approved for this approach, or is it just a good habit?"
I don't know what vertical nav is. I can't fly LPV with my kit. On a nonprecision approach, one manages the descent oneself, as per the approach plate. I check the altimeter against the GPS as a habit, in case the wrong QNH was set. In countries with poor ATC ELP (which sadly includes France a lot of the time) one gets all kinds of chances for misreading. Often the ATIS is illegible also, especially in France. But it is also easy to set 1005 instead of 1015 etc. If the check against a (decent aviation) GPS fails then there is something seriously wrong. Units like the G496, and all IFR panel mounts, contain the geoid correction so they are accurate on altitude within 10-20ft. Phone and other consumer GPS are usually not corrected and a 160ft error is common around here.