I don't know the particular legs and head that you're using so I cannot comment on them.
I have two sets of tripod legs that I use with the SL + SL90-280 lens:
- Manfrotto CX190Pro3
- Feisol CT3442 Tournament with center column
..and two heads:
- Arca-Swiss Monoball P0 (with standard Arca-Swiss QR plate clamp)
- Acratech GP ball head (with screw-type Arca-Swiss QR plate clamp)
Normally the Monoball head is on the Manfrotto legs, all up weight 3.2 lbs, and the GP head is on the Feisol legs, all up weight in the carry bag 4.1 lbs.
The Manfrotto legs are rated for about 12-13 lbs and are convenient to use for table top and light field duty when I don't need much elevation (max height with extension is 56 inches). The Feisol legs are rated for 26 lbs and, with column fully extended, give me up to 74 inches of elevation (I need a step stool to see through the viewfinder); they're a bit slower in use.
Both tripods are very steady alone with the SL/SL90-280 fitted, with no assisting weights added, but both have hooks to add my camera bag or weights for additional stability in windy situations. I recommend either head and either of these sets of legs for this camera and lens. Beyond that, I strongly recommend sticking with the Arca-Swiss traditional type quick release clamps and plates: they're the lightest and the strongest QR pieces in my experience. A-S type clamps and plates are available from Arca-Swiss, Really Right Stuff, Acratech, and Kirk Photo amongst others.