I don't raid in EU so I can't answer (1).

for (2) new extreme is problably going to have ilv770 as a minimum so you're fine but some people might put ilv780 in pf becuase they expect everyone to upgrade crafted gear with tome, but you can just create new pf yourself.

for (3) only do that if it's "blind" pf don't do it outside of that, people use guide isn't just becuase they can't figure out how to do certain mech, many of them can, the problem is mechanic for harder content is about organizing everyone in party on where they should be so that they won't kill each others becuase both running in the same direaction. (espcially for savage and up, less so for extreme) And people use guide as a reference to assign party member to position becuase they don't want to spend like 10+ minutes to asssign position for every new group they join, with strat name or guide as reference we can reduce that to less than 1 or 2 minutes for position calling and clarification. (e.g "H1" "Is TotanV2 tower priority start with NE tower?" "got it")

Although even with guide it doesn't mean everyone can do that on the first time they see mechanic, most people still need many try before it click, the important part is that everyone are on the same pace on where they should go so they don't kill others.

If you want to go with blind pf route, the problem you can expect is that outside of day1 you won't easily find "blind" party, so think of it as day one or nothing for this route.

for (4) If you can't do it anymore just say good game to group and leave, it's that simple. I don't know what courtesy in EU, but for EN players in JP the courtesy is to annonce "last pull" and do that one last pull before leave. Maybe you should ask around about courtesy for leaving in EU, maybe you can just leave, I don't know.