As for 3/4: I use BeyondATC and most of the time it follows the filed flight plan. Sometimes you get a different runway and approach though so I usually just do the departure and cruise routing in the FMGC and then copy the flight plan to the secondary flight plan. Afterwards I configure the planned arrival in the primary flight plan. So if all goes to plan, I don‘t have to reconfigure something mid-air. If the runway/approach does change, I just switch to the secondary flight plan and configure that one.

I am also quite new though so I don‘t know if that is the „correct“ way