Diskless rocks for making appliances. I have rock solid raspberry pi based micro-sd based services because of this - diskless mode keeps the sd writes to a minimum. unplug the power at will? sure, go for it.
I had something similar with a TSA event in the late 90s. My buddy and I took second place in the nationals for Computer Construction. We asked "why didn't we get first place?" and the response was "because your inventory had serial numbers listed. No one does that."... which was jaw dropping, because both of us had receipts from recent purchases at computer shops were every serial was tracked. Near the end of the event we found out that the judge of the computer construction contest was a teacher at the same school as the winner. Our teacher did nothing to contest it as we had a flight to catch. -sigh-
Of everything done, doing nothing about something "so that I can be home at night" still places highest in my list of challenges with software engineering.
Answering the first question - the keyboard... pro's type, a lot. It'd be fantastic if they had decent keyboards... full spherical keycaps and travel. None of this flats and scissors mush... I gots to type brackets and braces for a livin', yo.
For the second... depending on your eyes, get the retina display. For most people, its worth it. If you wear coke bottle thick glasses in 2014... maybe not worth it. Fitting more characters onto the screen and having the text rendered ever so properly is lovely for writing code with.
If you run VMs, the i7 is handy. Otherwise, the i5's are pretty rocking as is. I always go with multiple power adapters... but you can stock up slowly on sales and ebay if you're not already living la vida macbook.