Rebuilding interior walls

You do need a building permit. Your contractor can get any required plans and get them filed with the city.

Your co-op's alteration agreement probably has something to say about it. (The co-op owns the building, not you, and has to deal with the mess if you try to get around things.)

My contractor would handle getting architect-stamped plans and expediting? Is it cheaper if I hire architect/expeditor? What sort of money are we talking about? So helpful, thank you.

Dkarchmar,

The first thing you need to do is talk to your buildings management co. They might or might not need to have a permit for this.
If you need a permit ask your contractor to reach out to any architects they know and you should also price it out yourself as well.

Dkarchmar,
If you're done, could you post about your experience? We are facing the same task and would love to hear how long it took you, who you used and the approximate costs. Thanks.