a) look here.
b) BUCs are available from Amazon for under $100. Avoid anything smaller than a 3.5" monitor
c) Kinda hard to say what mine cost because I have a lot of pieces laying around. The camera and transmitter are from a Peak PKORG but I used the mirror on my RV. The Monitor is a 3.5" from a VR3 system. Many seem to use the same wireless video technology (including my TV sender and a number of CCTV systems).
Did need to drill one hole for the cable/grommet behind the license plate. Tap into the white/green stripe-black pair for the backup lights. NB.
d) Guesstimate: about 400x300 pixels - enough to see a child or dog but might miss a squirrel. Wll be better when I obtain a radio/dash display.