Hello. I'm trying to upgrade my staircase from wooden balusters to wrought iron rails. Once the balusters are removed, there will be holes on the treads in the areas where they were sitting. I'm attaching a similar photo to my dillemma.

This leads me to two choices. Cheaper: Figure out how do fix / repair the holes, or Expensive: Add or is it Raise a stringer on the right side and have the wrought iron sit on the stringer instead of on the treads.

I will not be doing either myself (I have no experience with anything wood related.
Question #1: What is the best way to repair the holes and not have it look like a "shoemaker's job". (no offense meant to shoemakers)

Question#2: What is the best way to add the stringer? Who do I hire - what type of carpenter? I'm in NYC and I called 2-3 stair places and none wanted to take upon the Stringer job - they said they can build 3 staircases in the timeframe this job would ake.

Would appreciate any suggestions and advice to this dillemma. Thank you in advance!