http://www.totallytanked.co.nz/redear/ Here is a RES turtle care sheet, written by members of this site if you want to have pet turtles in a proper, healthy setup.
A 6ft would probably be too small for turtles and cichlids anyway. Remember, turtles need a basking ramp so you'd only be able to have the tank about 2/3 full, taking away lots of the fish's space. + having a glass lid on a turtle tank isn't very good, it causes condensation which stops them from fully drying out. They need to dry out to keep their shells healthy and in good condition.