setting up sump....problem.

my tank isnt cut and it has a wide glass lip around the top with the corners cut out, i have no chance of hanging my skimmer on the side so i thought id set up a sump, the lfs advised me to use maxi power heads and pipe and a controller, but today i went to a different fish shop and they said its VERY risky. what return flow would i need? are there any other options? i would like a sump for other reason aswell......any help would be very apprieciated.

tank is 5ft. the sump will be directly under the tank, and i havent ordered the sump but it can only be 2ft long because of the cabenet has a partition.

also, i wud love a hang on overflows, but there is that glass lip on the edge on the tank so its impossible....