You will have no issues fitting everything into the Antec 902 (specially the motherboard)
I was also going to ask, on the RAM...
If I buy another 2 sticks, would I need to change anything further? Should I buy the same ram...?
You will need to buy the same exact RAM (model # and all) to not have to do anything further (ideally). There are times with 8GB of RAM, that some motherboards require a slight voltage increase to remain stable with all four slots full.