First I would get the live rock with no aptasia. Second The sand from HD is fine the silica will just cause a diatom bloom untill it is gone (should be by the end of your cycle or shortly after). Third I wouldn't worry about a sealed container, you want a way for air to get in as the watter is taken out to avoid a vacume effect I would just ust a small pwoerhead connected to the float switch in whatever manner is suggested by the switch manufacturer. and on the skimmer I am sorry but I can not help you there!