I got $40 on a card, what can I get on Newegg (ram)?

I assume your Windows install is 64bit?

PSU is fine

If you want to increase your RAM, you should buy an 8 GB kit, but that will probably put you over $40. It's not recommended adding mismatched kits in DDR3, it will cause performance and stability issues.

Otherwise, you'd probably be better off getting a Joystick, or controller or mouse/keyboard. System is sufficient for now, when you are ready to upgrade in 2-3 years, you may as well do the whole thing at once.
 
If you can spare $10, and you probably should, then this is about as well as you can do:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231536

DDR3-1600 at 7 latency will compete with most anything out there speed-wise.

If you're really on a strict $40 budget, you can try this with a 9 latency that will be almost as good:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231428

or this which is also a 9 latency but DDR3L, which could eventually be used on a Skylake build if you're looking that far ahead ...
http://www.newegg.com/Product/Product.aspx?Item=N82E16820226691
 


Yes, but it'd be a waste. That 3-stick set was designed for systems that support triple-channel memory, and I believe the last of those were around 2010 with the LGA1366 socket Bloomfield CPUs (i7-900 series) and Gulftown (6-core version of same). Your AMD setup is only good for dual-channel, so it will get best results with 2 or 4 sticks; if you use three sticks it will just disable dual-channel. I would just go with a good 2x4 GB set and call it a day.