The benifits of a sump will add numerous benifits to your tank. Benifits,macro algae,filter socks, water voluume to system etc.
Number one simple & easy, water going to a sump is usually just gravity fed. If you an overflow box already
Overflow for Wet/Dry
The return pump is what actually allows the water to return from the sump.
No water coming out from the sump meens no water existing the overflow/tank into the sump.
As complicated as a sump may seem there are quite simple.
As answering your question to what protein skimmer, the coralifes on sale are a great buy & worth the money. My 125 coralife super skimmer was $114. The most cost effecient with the highest ratings would be the Octopus skimmer. Most are sump skimmers.
Now out of the 3 you listed, I personally do not care for the turbo floater,poor reviews, the aqua c is an injection fed skimmer...more maintenace on the skimmer due to the injectors.
Deltecs are top notch equipment, pricey & may do ok but personally you would get double the performance from a sump skimmer
There are very few hang on skimmers that will come close to the performance of a sump skimmer
Return pumps you won't go wrong with a mag 7 or 9