You don't need i3 and 8gb of ram. If you are focused on gpu mining you can go with celeron g1820 (ones i use for lga1150 socket) and 4 gb of ram. There is no need to spend extra money since those don't impact mining performance. Anyway based on your questions it doesn't look like you did much research on gpu mining. Maybe is better to make 1 rig first and then if you are able to manage it expand ?