Hi,
I'm replacing an old cast iron drain stack with PVC pipe.
I don't plan to make any major changes to the layout.
I have attached a pic of the proposed setup (not to scale).

I would appreciate any comments.

A couple of things:
1) The existing kitchen sink was direct vented into the main vertical soil pipe. I will need to update this since this is against code.

2) There is an existing iron (black pipe) vent pipe that connected to the main vertical near the basement floor. It has an access opening available at kitchen floor level to the left of kitchen sink. I could potentially access this to vent the kitchen sink.

3) The 1st floor bathroom sink has an AAV.

It is difficult to see details in your drawing. But in general, just follow the original installation and you should be OK.

If the work is being inspected, as it should be, there is a chance inspector will ask you to install new drains as per current Code as - at least in my area of operation - stock venting and AAV vents is are not allowed.

Important: Make sure you support cast iron stock pipe before you start cutting. Also, I suggest you start cutting from top towards bottom.

Good luck with your project

Milo