Hey Contacttower -
IFR Flight plans nothing is required if you stay within Europe.
FIR's for departure and destination are automatically added to any VFR flight plans.
But if you fly across any countries and do not land, then you need to add these FIR's. Skydemon is a great application that does lots of VFR flight planning and starting Jan 1 it will allow filing internally, using EuroFPL partner services.
I use the additional addressing feature of EuroFPL when flying in SE Asia, where EuroFPL doesn't yet provide fully automatic addressing. I also use it to send a copy of the flight plan to handlers.
And absolutely, for vfr to/from ZZZZ airports, you need to identify a nearby ICAO airport and manually address that airport (ICAO code + ZTZX, ICAO code + ZPZX, and FIR code + ZQZX) so your flight plan goes where it needs to go.
Thanks
Travis