XDJ-RR (Adding Turntables, 2nd Master, Locking Deck)

Hey guys. 

Got 3 x questions I cannot seem to find the answer too

1/ Can I set up a second turntable ? I can set up 1 using the AUX power. Is it possible to do 2? 

2/ There is a phono Master & an XLR master set. Are the second ones usually used for something?

3/ I keep stopping the deck that is playing by accident. Can the deck be locked to prevent this ?