Which Macbook Pro Retina For College

Im going into college in January, and plan to switch from my lenovo laptop to a macbook pro with retina.
I had a few questions considering this is going to be my first mac ever. i5 or i7? I know from reading that you cannot upgrade the processor or ram after purchase. i plan on using this as a programming platform (ios apps and video games). Also, will 8 gigs of ram be enough? Or will 16 gigs be required? Space isn't an issue because i have a primary machine for my main needs, and if need be i can get an external hdd. Thanks in advance for the help! Also if possible, can i get a macbook air as a substitute? (most likely not going to happen, just out of curiosity)

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