Is this a safe plan of moving my tank ?

[FitoPharmer]

You should be fine. I move my tanks all at once, but this way your adding an extra level of safety.
To help you with the sand I suggest you siphon it out of the tank with a 1/2" hose or something. If there are no large chunks its vacuums out very easily. When I siphon out any sand I always give it the smell test and the partical test. If the sand either smells really strong unlike the LR, or smells eggy at all I will discard it and use new sand. Also if the sand contains large amounts of detritus particles I will wash it in saltwater from the same tank, or discard and replace it if there is too much to rinse out.
I find large strong bags like ziplock freezer bags work wonders for adding sand back into your tank with little sand storm as possible.

Also the regal tang likely will not do well long term in a 56 Gallon tank.
http://www.liveaquaria.com/product/p...330&pcatid=330