I can't answer about the carryons, but I can answer about the lounge.
A fair number of times, in both AMS and IAD I have gone from either checkin or plane to lounge and then lounge to plane, and I have gotten wheelchair assistance both ways and no-one raised an eyebrow - everyone seemed to think this was standard. In fact, in AMS, when I did not have lounge access and I had a long layover, I was parked in a special area and they came back for me later.
So, go ahead, go to the lounge and continue onto your plane later.
Jaelle