Are you sure the cameras are going directly to the monitor and not to a quad/mux/dvr before they hit the monitor? 500-600' should not be a problem, I assume you are pulling RG-59 to all the cameras. Worst case you can put an amp at the head end equipment if you see some signal degradation. If you wanted to be proactive you could pull RG-11 to the further cameras, RG-59 has a 20awg center core whereas RG-11 has a 12awg if I recall correctly, all you are dealing with is voltage drop in the signal. If the cable is unterminated at this point you should try to install two or three piece BNC connectors, not the twist on types, I have cut off hundreds of the twist ons. You do need a crimp tool for the multi piece connectors, but they are not all that expensive and are can be picked up at almost any supply house or even HD or Lowes. Another option which was suggested was using baluns on some sort of twisted pair, normally CAT3 or better. This can help cut down on the length of your cable runs if they have some house pairs you could cross connect on to. Running a CAT5 to each camera also gives you three extra pairs which could be used if something happend during the pull and you have a bad pair or if they decide to add cameras later on the cable is already in place. I just finished a job at a convention center with 64 cameras on active baluns and there were runs over 2500' with no prolems.

As for the power, if these are fixed cameras with heaters in them and the run is around 100' you should have no problems with 16awg power cable, you should even be ok up to about 250'.