i use 5-3-2 with roma with a sweeper, wing backs, wrong footed inside forwards, and a deep lying false nine. here's a screenshot and i'll try to keep my explanation short
with totti as a static false nine, he draws the opposition DC's high up into midfield, giving space for my FR and FL (vucinic and dos santos) to make diagonal runs into. notice they are wrong-footed inside forwards, so they are usually shooting from their preferred footing. mexes as a libero acts simply as a box2box defender, right behind de rossi, who's a box2box midfielder. i have pizarro set to a static deep lying playmaker role to keep possession. ivanovic and criscito doing a simple defensive job. anyukov and riise provide width.
the good thing about a libero is that he helps keep possession during the attack, and provides extra cover when defending. same as a box to box midfielder IMO, except more defensive. the good thing about FL and FR's are the runs they make into the area between fullback and centerback. most teams play with attacking fullbacks, which plays into this tactic
with wingbacks, sweepers, inside forwards, and box2box midfielders, i feel that this formation provides me a lot of movement and fluidity. i only have pizarro and totti static since they have low stamina, and not surprisingly, i have pizarro as the playmaker and totti as the targetman.
not sure why or why not to have a sweeper keeper. didnt make any significant difference to me when i toggle sweeper keeper on/off