A)No and Yes, Just make sure whatever power supply you buy you get one that has a 24 pin connecter for your motherboard(or you can use a 20 pin with a seperate 4 pin connector to make 24, your choice) Basically if you buy a new ATX do not get one with only a 20 pin connector. It has to say it supports a 24 pin connector regardless. If the new Atx says it supports both 24 pins and 20 pins than your in the clear
B)Could you Rephase that statement, I didnt understand it.
C)I dont see why they wouldn't. They; Are you talking about EVGA? The manufacturer of the video card? Give them a call and see. You need a 6 pin connector for your video card, why would you need to extend that? Im just curious.