Question: What is the longest run of RG59 you can have without loss of signal

Answer: RG59 cable will typically carry video signal up to 200 meters or 650 feet, without signal loss.
If travelling further than this, CAT5 should be used in conjunction with video baluns. Over 200 meters, you should consider using an active balun (video amplifier) at the camera end.
Wherever possible, power should be supplied locally to the cameras.