Good evening,
1) Yes. Basically you don't want aircraft in the sensitive area when an aircraft is approaching during CAT II/III approaches (protection of arriving A/C) (LLZ&GS signals)
2) No. The approach plate (Jepp) tells you what's allowed and what's not allowed. ATC will also tell you if it's Low Visibility procedures that must be applied or not ("LOW VIS in force").
3) Not neccessarily. Some A/C require that the AP is on (most), some that it is off. Airbus, Boeing (
afaik) & Avro's have it on. Then some have a HUD which requires that the pilot flies the approach manually (some Swedisch turboprops).