Thanks for posting in PVGBBS. Basically, your steps are correct. I will follow your steps to explain more details for you.
1) Go through Customs (How long would this take?)
It depends. It is not far from most boarding gate to the custom (about 500 meters I suppose). Based on my experience, 15 minutes will be enough. Of cause I cannot predict the length of the line waiting for the custom.
1.1) Step into the luggage claim hall.
You may not need to claim your bagge there.
1.2) Step out of the International Arrival Exit.
2) Exchange US dollars for RMB
You can exchange for RMB at the bank just opposite to the international arrival exit.
3) Was 5) Get ticket to Shenzhen at China Southern counter (Where would this be? same buiding?)
This should be before you buy the construction fee. The Counter for all airlines are on the Third Floor of the same building. You can take elevator from the Arrival Hall to Departure Hall.
The picture above shows the arrival hall. I don't know the counter for China Southern Airlines. But it SHOULD be somewhere at Ticketing Island A to D.
3) Buy Airport Construction fee ticket
Yes. 50 RMB for domestic flight.
4) Go through channel using my Construction fee to domestic area
6) Go to gate.
The other steps are all right.
Note: Please check whether the flight for Shenzhen is at Pudong airport or Hongqiao Airport. Shanghai has two international airports. It is sometimes confusing. There is about 1.5 hour bus ride between the to airport.
SHA is for Shanghai/Hongqiao
PVG is for Shanghai/Pudong.
Good luck!