Nicholas's public residence is located in a secluded, rundown apartment building somewhere in the suburbs of New York, where he generally entertains ordinary wizarding friends.
As for No-Maj friends, well, MACUSA does not allow wizards to have excessive interaction with No-Majs, or the ministry's employees wouldn't mind taking you to prison for a little chat.
The spot where the four of them Apparition-ed to was near this old apartment building.
Chapter 446