A few Questions

Ive got two questions I want to ask about when I got to Spain in two weeks time:
1- Last time we flew 2 sectors with BA we checked in at Aberdeen all the way to Faro, without the need to re-check in a London gatwick. However, this time we booked ABZ-LGW, and LGW-AGP seperately. Does this mean that they won’t be able to check us in right through as it is two seperate bookings?
2-The new airbridge that has recently opened at gatwick, is anybody allowed on it, or are you only allowed accross it if your flight is leaving from the gates that it connects to?
(I know I said two but I have one more question)
3- LGW-AGP for the 9th July is an A320, but on the 16th it is an A321, whereas on the 23rd july it goes back to an A320. Is there anychance that the 9th July could be an A321 aswell?
Thanks for any answers received
Tom