welcome to canreef,you sure picked the right forum to share your build.
From looking at the photo you provided one thing I don't like is your foam pad looks old and beat up I would get a thicker pad and a heavier gauge. From experience I like using the egg crate glued to the bottom of the tank as it gives support for your rock work, for filling the tank I would place the sand on the egg crate and have the RO hose right into the tank, yes it will take a couple days to fill but slowly without any storms
. Enjoy your build.