re: Would you do 7/1 ARM or a 30-year fixed mortgage for a starter home?

I regret not doing an ARM. It would have worked great for me. Similar to you, I'm not planning to be here long term.

You should also review the loan terms. Most of the time there's a max yearly increase, and a maximum overall increase. At 3.4%, it should not creep up much over 5-6%. Take advantage of the lower interest rates for the first few years, and not pay much different than a refi at the point it starts climbing.