If I am fishing saltwater then I prefer a 3'-4' fluoro leader. If I am fishing for bone fish, then I like a 6' to 8' leader. I have never found any benefit to using fluoro in freshwater. Fluoro absorbs water and makes that section of line slightly heavier causing a bit more sinking which can be an issue if you are trying to use a floating bait.
No swivel is needed and braid and fluoro are best connected using a Uni to Uni knot.
Capt. Craig Copeland
2013 Nautic Star 2110 Shallow Bay Boat
Nautic Star Boats Pro Staff (nauticstarboats.com)
Redneck Fish'n Jigs Pro Staff (redneckfishn.com)