You can always purchase external hard drives if 256 isn't enough for you. I've had ~250GB on my back-up Windows laptop and 250GB on my 2009 MBP, and they've lasted me a solid 3 years.
Mind you, I have tons of music and pictures on both laptops. Displays shouldn't demand much space. If you think about it, major applications may demand max 4-5GB of space, something which can be willingly spared. Unless you're a video-editor, I doubt you'll need a ton of space. If you ever do need space, get external SDDs.
Oh, so you ordered a Retina eh?
You're fine with the 256GB storage.....Here's what you do, take the hard drive off your old macbook, put it in a USB external enclosure and use that drive to save all your pictures and files in.
That way, you won't have to worry about filling up the 256GB flash storage in your Retina.
I think that 256GB would be just fine. I had a 120GB drivve on my old 2006 MBP and just had to store my iTunes and photos on an external drive. I have a 512GB SSD now and I store about 170GB of music on it with the rest on an external HD. If I subtract that from the remainder used, I'm actually only using about 131 GBs.
So my opinion is that you'd be just fine.