a few questions about GTX 960 and 970

These cards are generally quite. The noise level will vary depending on which version of the card you get. Most non reference cards and Overclock very well without getting too hot. The gigabyte g1 would be my recommendation for both 960 and 970. If you plan on getting 960, I would consider 380 and r9 280x (280x should be the best performing one). If you plan on getting gtx 970, the r9 390 is a good option as well (390 would perform better at 1440p but not as good at 1080p compared to 970).

Here's my answers:

a) It will depend on the brand. MSI/Asus usually have more quiet cards; Gigabyte usually have noisier cards. But like I said, it will also depend on the brands' specific models. Some brands make more than 1 model of the same GTX 960 or GTX 970 and there are differences in noise, temps, performance and other factors per model.

b) Yes, you'll need a CPU Cooler if you are going to overclock. If you'll do light to mid overclocking, an air cooler will do. If you'll do serious overclocking, a liquid cooler is highly recommended. Performance-wise and noise-wise there are a LOT of brands and models to choose from - each having their own advantages and disadvantages. The most commonly specified air cooler is the Cooler Master Hyper 212 Evo, having a very affordable price that does its job well. However, if noise is an issue, you might have to select a different brand or a different model. The most important aspect of air coolers, aside from airflow, is the coolers height. Not all air coolers will fit in a given case. You have to check the interior dimensions of the case you have if it supports the height of the air cooler you want to install. For liquid cooling, it will come with a small pump/contact + a radiator with fan/s. The advantage of the liquid cooling is that it won't take up space in front of your motherboard. These radiator with fan/s comes also in different lengths (usually 120mm, 240mm, and 360mm). Like the air cooler, you have to check the case if it supports the mounting of such radiators. The air coolers (or the pump/contact for liquid coolers) are installed above the CPU, usually comes with a bracket with holes installed at the back of the motherboard behind the CPU socket for plugging-in the air cooler or pump atop the CPU. The radiators and fans are usually screwed on the case in the fan slot you choose. When you buy such coolers, it'll come with a detailed instruction sheet on how to install them (as each brand may have different methods of installation.)

c) For the GTX 960, the AMD brand that has the same price but better performance is the R9 380. For the GTX 970, its the R9 390. Take note though that the AMD's would require higher PSU as it draws more power and has higher temps than the GTX's.

I would stick with 3gb 280x as the card is not powerful enough to ever use all 6 gb of vram. 390 and 970 will last you longer as both cards are insignificant better than the rest.

It's not possible to mount Evo 212 to gpu. For multi card configurations, I would go with r9 390 for extra 4.5 gb of vram over gtx 970.