the over flows are on the side for a few reasons
1 better flow
2 to make the base stronger to allow a 6x2x2 sump
if you look at the over flow boxes you will see 2 return pipes in each over flow box 1 pushing water to the front of the tank and 1 to the back
i will be turning over 20,000 lph so each over flow box has 2 x 40mm drain pipes
i think this will work well but we will see
as for putting the aro in i will be using 50l of mature media from my set up now another 4,000 bio balls and some jap matt
i will also be using seachem stabilaty for the 1st week which will speed up the cycle