Yes you are limited by the rating of the panel. The compressors should have start up delays on them so that will help you out with that power failure thing and the heaters are pure resistive loads. You are being somewhat conservative with the 1P loads counting all 3 phases when you are using 1 or 2 but be sure you balance them as well as you can. I think you will be OK but that is really a Scott question when you get to this "design" stuff.
