Death Watch seemed like a fairly sizable organization. I don't know if I would call it a full blown army, but it was definitely a powerful faction.
The Mandalorian seems to be based on the live action design from the flashback scenes in The Mandalorian series on Disney+. While the coloring is similar to the Death Watch armor in the Clone Wars animated series, the Death Watch members in CW have armor that's much more like that of Jango Fett in appearance.
As for these reveals? I'm very happy to see them - especially Ahsoka! I was concerned that it might be a while before a Corvus Ahsoka would come out, and Hasbro would try to get people to buy the retro collection version because of FOMO. But this a fantastic representation of Ahsoka from The Mandalorian.