I have an existing opening in a non-load bearing wall

of around 12 feet wide and want fill it back to a solid wall.............then, I want to cut and finish an eyebrow arched opening.
The arched opening would start at 42" off the floor and be around 6.5 feet high and 8.5 feet wide.

. This second photo is reversed looking back into the living room from the kitchen side of the wall.
It just doesn't seem like that tough of a job. Here are my thoughts....I would like to hear yours!!
Tear out drywall down to bottom of existing opening.
Build a header across where the top of the new arch would be.
Frame in wall to fill opening above.
Cut opening as needed below new header.
Re-route wiring to allow for new cable lighting system. (No other electrical)
Install arch kit and replace drywall. I was planning on leaving the existing drywall in place below the 42" level and having a seam at that point.
I am guessing the toughest part is the drywall finishing/taping and where the new drywall would meet the ceiling.
Any idea on what this should cost me to have done versus tackling it myself?
Oh, I am new here and this is my first post................thanks so much...