1. The PSU should be OK. Use HWMonitor to check voltages
2. Your PSU should handle 280X/7970 CF (They are the same card). Sapphire is considered very good for Radeon cards. And you sure should get a 1080p monitor.
3. Yep you should upgrade - AMD FX-8350 or Intel i5 4670k at least. Especially if you have CF 7970/280X
sorry for the long reply, since I was looking at some of the parts that you suggested, and I agreed that for the 280X I need to upgrade the processor including the motherboard too, and so far I will pick the Sapphire Radeon R9 280X 3G GDDR5 TOXIC, and the FX 8350, and as for the motherboard, I'll pick the GA-990FXA-UD5 model, but it seems in my country, neither of the GA-990FXA-UD5 nor GA-990FXA-UD7 are available anymore, if you don't mind can you give me another recommendation for the motherboards model that I can look for?