After making several high gravity brews, I would not try to mash 18.5# of Pale Malt and expect to hit my gravity. I would drop out at least 6# and use Malt Extract and maybe a little sugar to replace it. An estimated FG of 1.041 seems way too high for me. I would play with sugar, mash temp, and yeast to make sure I finished at least in the 20s. Also, 10 grams of gypsum seems high (although it is a hoppy beer). If I was doing salt additions, which I usually do, I would want some calcuim carbonate (chalk) with all those dark grains. I use Palmer's spead sheet for salt additions. Just a few thoughts.