I store my filters in the Lee Multi Filter Pouch and well, all 10 pouches are filled with Hitech filters
The Lee filter pouch is very well made and I can recommend it. For the foundation kit + 105mm pol filter I also use the Lee pouch.
I do use the Lee foundation kit with two filters slots and the 105mm filter holder attached to it. I use an older 105mm Sigma EX pol filter for about 50% of all landscape shots.
For a test shot a minute ago I attached for the first time the wide angle adapter ring (82mm) to the Tamron SP 24-70 mm lens. In front of the lens was the Lee foundation kit + 105 pol filter. A little bit of mechanical vignetting is visible in the extrem corners from 24mm till ~33mm. At 35mm the vignetting is gone. But I normally use the TS-E lenses for such applications. With the TS-E 24 mm L II vignetting occurs at 5mm of shift.
A reverse grad ND filter is a special filter for sunsets and sunrises. The Hitech website says:
"The reverse grad is a vital tool if you are looking to take sunrise or sunset shots. This is because the ND part of the grad is upside down, with the darker part at the middle of the filter and the lighter part at the top. This ensures the maximum light reduction when the sun is at or near the horizon." I couldn't describe it much better.