Are you on Instagram? If so check out Thirsty Gallerina, she gives info on free gallery openings even with icons that show which ones have wine and bathrooms
Also it's not just art but secret_nyc is good too.
https://www.instagram.com/secret_nyc/
There's also ArtCards which is a weekly email.
For lectures maybe get on mailing lists at places like Cooper Union, the Met and other places that have free stuff. Hope you already know this but you can get into the Met bascially for free as a NYC resident, just have to show an ID and give whatever donation you want - even 5 cents.