Both look like dowitchers to me.
Stilts would have a little shorter bill and would not have that grayish neck and upper breast this time of year, which is typical of dowitcher.
Yes, a good field mark for WTHA. Now that I have the image on my computer screen instead of a smartphone, is that a white breast patch or are the feathers being blown out by the wind revealing the underside of the feathers?
Yes, I think you have a L. Scauup there. Coloration/contrast look good, as does the peaky crown and bill shape.
There are some male mallards among the bank ducks, and there is a good chance they are all mallards.
The back duck in the bottom photo appears to be a scaup rolled onto it's side for grooming. I can see a yellow eye on one of those foreground ducks, without an eyering. That is likely a scaup also.
The dark cap, head profile, and facial spots arrangement look better for Surf scoter here. I couldn't detect any white in the wings where it should appear on a WWSC.