This is a fun story to read, and I'm looking forward to seeing how it concludes.
Whilst I can appreciate that you say your fixed-wing experience is quite meagre, you are a CPL(H) and instructor as I understand it. This implies a familiarity with certain basic aspects of pre-flight planning. Strangely, many of your workload inducing issues appear to be related to planning problems.
For example
- routing Echo followed by Sierra is the standard *documented* departure from Tours for points south. You'll find it in Bottlang and in the free online AIP. The routing exists to stop you busting the ZIT near Sorigny. EUR 150,000 fine for that offence.
- La Baule was NOTAMed with parachute activity on the day of your flight (I was also in the area)
It is tough to tell from your write-up what kind of pre-flight planning you actually perform, but perhaps a little more would lessen your workload?
2D