I think I understand pitch now. Basically the same thing as toe-in or toe-out, the intent of which is to get the barrel and sights level and perpendicular with one another in the vertical plane when you are in shooting position. Since shotguns are shot very often with your elbows out (so you can swing easily, a toe-out configuration works pretty well. Rifles are often shot with your shoulder elbow down, so often a toe-in is needed to gain alignment.
If you do your build with a 3/16" cast off, and a 5 degree toe in, the toe winds up being pretty straight back fron the barrel but a bit twisted. That is or can be slowly "unwound" as you make your way forward to the rear foot of the TG.
Yes on comb angle. Since recoil wants to drive the gun straight back, it will. Since your shoulder is below the bore, it forms an angle, and the gun wants to rise due to the angle. Since there is already a built in angle to the comb, just coming straight back is going to raise the stock relative to your cheek, Add in the anchor point of your shoulder, and there is muzzle flip induced. Both forces combine to whack your cheek bone. The greater the angle, the more the whacking.
That's why the M-16 was designed as it is. The bore axis is directly in line with the shoulder, so it wants to come straight back. (Dangerous game heavy rifles are also made with a minimum comb angle too.) The human form of our eyes being placed higher than our cheek bones is accomodated by the high raised sights on the gun, and recoil is better tamed. That is particularly useful when trying to control the weapon in full auto mode.