Various new mining questions (What GPU to use, heat questions, riser questions, etc.)

I'm new to serious mining (I've tinkered with GPU mining on my GTX 1060 just for fun but I know it's not profitable) and I'm considering building a cheap rig with used (or maybe new) GPUs. I have absolutely no clue what I should buy; should I buy a more expensive recent GPU or an older GPU that is really cheap, or somewhere in between? Are there specific models you look for when building your used rigs? What should I buy as a newb to serious mining?

I'm interested in mining ethereum since I've read it's profitable on GPUs. I don't want to spend too much on this but the rig needs to pay for itself within a year. Electricity here is about 10c per kwh (USD)

Another thing I'm concerned with is heat. It seems to be one of the factors that isn't mentioned too much. If the rig is putting out a ton of heat, it will raise the electricity usage from the AC. Where do you put your rigs to avoid this? (I've also read you can use them to heat your house in the winter, so would this save a significant amount on electricity in the winter?)

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Right now I'm strongly considering building a rig with 2 RX 480s. Here's my rough part list on PCP: http://pcpartpicker.com/list/nw7h3F

The motherboard is kindof iffy, but it seems people have had success with it. I know I will need powered risers; how do these look?

If my math is right the rig will pay for itself within 183 days, excluding electricity cost.

Do you have any part recommendations? I'm trying to build it for as cheap as possible, so down the line I can add more GPUs to the setup on new motherboards for minimal cost.

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Another question, should I mine ethereum or ethereum classic?


Thanks! Sorry for my newb questions

edit: bolded the important bits so it's easier to read this wall of text