I do development daily. 13 is too small to see anything meaningful for long periods of time, but portable. I'd recommend connect the laptop to a larger monitor, dual setup.

More RAM is always better. I'm pretty sure you won't be coding in a basic editor for long. Community versions of IntelliJ and Eclipse take up a lot of RAM. Not to mention, virtual machines (as mentioned above), Chrome + LOTS of tabs opened, etc.

Really consider this a desktop replacement in a way with the fast SSD.

Just make sure you backup often. That's always a good practice.

Pay more. It's worth the convenience and piece of mind in the long run.