Are Architect's plans required for kitchen reno?

If you are not moving any of the appliances you should be fine

Tearing down walls will require Architectural plans,at least my board does. If your keeping the same layout and if you are in a post war building which means you have negative air pressure, and your not touching those then you should be ok. Moving around walls, creating openings and messing with the duct work will require such plans as well as DOB filing.

It's about wall structure also , some Co-Op's care about that

Some coop could require you to file with dob - usually in case where risers are being replaced inside demising partition, in any case you should submit to the board for approval before you start any kind of work