I have been to many private events and parties ( several times per year over several years) at Maggiano's in Hackensack.
I've seen them handle holiday parties, birthdays, wedding parties, corporate merger events, christening parties, Bar/Bat/Bas Mitzvahs, etc...
Their private rooms are adjustable in size and soundproof, their banquet staff is as professional as they come. I have heard nothing but good things about the food and its presentation. If entertainment is wanted, they have house bands, DJs, Karaoke Hosts, etc.
Given the description of your needs, I think this place will fit the bill perfectly.
While I have had dinners their and found the pricing reasonable, I have no knowledge of their party pricing- up to you
Before you ask, I am not an employee or owner, but have provided entertainment there on many occasions and found this place to be very good at what they do. If they weren't, I would hear about it. I'm just adding my opinion into an already positive mix.
I name this place first because I think their food is a few steps above some other venues that I've worked.
You can certainly go even more casual and get a private room in most places, but I am working only with the info provided. If you can post the type of event I may have other suggestions.