Go with the 400a service, no doubt something will be added. With all that floor space 10kw may be a little light for a guess on heat strips anyway. As far as baseboard outlets, if you can(do) use plastic boxes, carlon makes an adjustable one with a metal bracket. I used close to 100 of them on the last house I did, you can put em in fast, let the carpenters cut the trim around them, then adjust the depth after the trim is up. A word of caution, Romex also makes a box that is adjustable, but not nearly as easily once the trim is up, take a look at both and the difference is easy to see.
