I am running N1 (mentioned above) as part of Ghosts of Saltmarsh - I stuck it where Salvage Operation and Isle of Abbey go. . .giving the PCs a choice. They did Salvage Operation, but then refused the offer to handle the isle to go check on the news of a friend in "Orlane" (I use a different name for the town), thus getting embroiled in the reptile cult (who are also trying to recruit the lizardfolk from U2 which the PCs are now friends of).
Very nice. Yes, AtCotRG and the U1-3 series blend together beautifully. I've done it, too...many many many moons ago.