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
Humminbird HELIX 12 CHIRP MEGA SI GPS G2N
Nautic Star Boats Pro Staff (nauticstarboats.com)
Redneck Fish'n Jigs Pro Staff (redneckfishn.com)