Hmm.. I don't have any experience with Coralife skimmers. However, If the water level in your tank varies even a few cm, that will be enough to cause the foam head to rise and fall as well. This could explain the skimmer overflowing as you had stated earlier.
I have to encourage your decision to add a sump. This will allow you to place your skimmer in an area of the system with a constant water level, which will result in better performance out of your skimmer. Not to mention it gets some of that "unsightly" equipment out of view and under the stand.
IMO you shouldn't fret about the sand bed, fine is better than crushed coral anyway. Deep sand beds can be more beneficial in terms of buffering Alk any way. You just don't want to disturb deep sand beds in order to keep them doing their job (buffer Alk and reduce Nitrates) other wise thats when you get into trouble.
There are some good articles around here on sand beds you may be interested in reading.