Welcome to Montreal! Fellow New Yorker living in Montreal here. My two cents:
I cannot speak for the hotel you mention. If you want to be more in Plateau, consider the recently-renovated ITHQ hotel. A friend is currently staying at the Hotel Spa Carré St. Louis and is happy there. Both places are right next to the Sherbrooke subway stop, but I have not stayed at either one personally.
Re restaurants:
Cabaret was just ok for me. Too salty. That said, friends had an excellent meal there so maybe it was just an off night when i was there.
Skip Toque. It just felt very generic and somehow forced to me. Nothing terrible, but that would be an easy pass for me.
Helicoptere and Beba are solid choices. Haven’t been to either in a while, though, so maybe things have changed.
Panacée is good, too. Lots of locally sourced ingredients that you might not get elsewhere. I’d put that above Beba and Helicoptere.
I also like Mon Lapin.
The upscale place I recently tried for the first time and adored is Alma. It’s seafood-forward Mexican.
As for more casual, my favorite is Tesfa. Definitely get the hummus. Sounds boring, I know, but it’s really, really good.
Folfol is the casual cousin of Damas. That and Tesfa could be good options for takeout.
I’m very fond of Larry’s for a light bite. Consider a movie at nearby Cinema Moderne.
Kouign Amann, which you mention, has what I think is the best croissant in Montreal. I like Hof Kelsten for pastries. You might want to try both Fairmount and St. Viateur to compare bagels and to see how they differ from the NYC bagel experience. And I second La Binerie for traditional quebeçois cuisine, if that appeals to you.
For ice cream, I love both Unicone and Swirl. Swirl is vegan, but don’t let that turn you off.
As far as stuff to see and do, I suggest a bike ride. I love how bike-friendly this city is, so very different from NYC. If you’re up for it, rent a bike or use Bixi (Citibike equivalent) and explore.