CPU and GPU for Build?

So here is the deal. I have an MSI 970A-G43, 8 GB RAM, and a Source 210. I need a CPU and GPU for gaming. The thing is I have a 1280x1024 monitor and I know right now I could get a 650 ti or 7790 and be good. But if (IF) I upgrade to 1080p later, the performance will go down. Could it work if I got another one of whatever card I get and crossfire them? Or should I just go for a card for 1080p? I am 13 and can't get a lot of money, so don't tell me to get something really expensive. And for a CPU, would an Phenom II X4 be good enough or should I get a FX-6300? What if I sold my motherboard and then got a FM2 motherboard and a Athlon II X4 750K? I don't need a full build list as I have most other things picked out. Thank you.

Either of those GPUs will play games at 1080p.

The FX6300 would be preferable, but either of those CPUs are quite capable gaming chips.

970 motherboard would be preferable to an FM2 motherboard. 970 is much more upgradeable. Better to stay on AM3+, because you could potentially upgrade to a 990 motherboard, or a octacore processor. And the aforementioned processors are better than the 750K.

If you haven't purchased these parts. Going with FM2 and a 750K would save money, and allow you to invest in a better GPU.

I have already bought the motherboard. So the 7790 is still good for 1080p? Would I have to turn the textures down if I got a 1080p monitor? I just don't want to get used to certain settings and fps on this resolution and then bring up the resolution and get lower fps. I think I'd father have the better resolution over high textures and fps though. I have a friend who may sell me a Phenom II X4 or X6 so I have to see what I can get those for and if it's not good I'll just pull the trigger on the FX-6300. Thanks for your help.