Hello and welcome to the forum! The desktop your buying is definitely a good choice although to answer your question, I cannot exactly say whether or not an RX 480 will be able to fit inside the case. There is one RX 480 model that has a higher probability of fitting than all the other dual-fan designs but it really is up to you.
Here is the GPU:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131706&cm_re=RX_480-_-14-131-706-_-Product
Some of the reviews say that this specific model runs on the warmer side, but you can easily fix this by removing the cooler and applying your own thermal paste. I recommend Arctic MX-4 thermal paste, any other brand will do as well and the good thing is that most thermal paste tubes are relatively cheap (by cheap I mean under $10). Best of luck to you and I hope this helped!