Calculation looks ok, but yeah, expect a call on turkey day and X-mas!
Also, why not do them a favor by up-grading the service. Two spots left you're going to fill.... They're gonna have to do it sooner than later. Don't know the service size, but X-mas could be a main trip. Both units and every light, plus some, on in the house. Who knows what else... Not to mention they may whan to add a 120v 15A, "Well sorry, you need a new panel for that..." Do the new panel now, and save the hassle of pulling out your own work for this stuff, to do it later.
Or, if the service is beefy enough, do it on a sub.....
