Alright, I'll start plotting some stuff up. I don't believe Grey Knights ever do service in the Deathwatch, depending on which source of lore you're going off of. Some will maintain that almost no one in the entire Imperium are even aware of their existence, except for save some very high up Imperial Leaders, and possibly some Chapter Masters. Aside from the fact that committing them to the Deathwatch then exposes their existence to other Chapters, there are other faults.

Point two is thus, they are part of the Ordo Malleus, the branch of Deamonhunters. They are literally the entirely military branch for the Ordo. The Ordo Xenos uses the Deathwatch, as their military. The Deathwatch are experts in combating Aliens. Grey Knights are not. So sure, a Grey Knight will certainly be able to fight Orks, but a crimson fist veteran will probably do it better. So, Grey Knights are not worth the same to the Deathwatch, as the other veterans, and it weakens the Ordo Malleus, to support the Ordo Xenos.

Lastly, Grey Knights are overpowered. Granted, we're all playing superhumans, but you'll be playing several power levels above us.

So, anyways, I hope with all these points, you understand why I say that there will be no Grey Knight's in this thread.

I will be playing a Carcharadon Astra, aka, a Space Shark. If anyone wants inspiration, I recommend any of the Deathwatch books. Forge World has some free pdfs that have chapter tactics for a lot of Badab chapters as well.