Let me fire some answers, hope I read your questions right
Just came back from a long trip...
1. The marker beacon receiver is completely independent from the ADF, as in all other airplanes to my knowledge - doesnt matter where and if you have the beacon set since the marker beacon itself always transmits at 75MHz...
2. Well, I suppose just to reduce the load on the A system, no need to keep it pressurized all the time since you have perfectly good mechanical uplocks.
3. Ground effect? Speed over Vref? All kinds of reasons, you can land without bouncing even without the speedbrake