I am trying to figure out how much should I charge a new client
for maintaining administering a forum site? I know the initial charges
would include license for threads, photopost, perhaps some of the other
addons. and of course the monthly hosting fees. but what do I charge
for the initial setup and ongoing maintenance. What is fair?

Several of us use the Fee Structure we use here:
https://www.ubbdev.com/forum/services.php

I take care of everything on an hourly basis and just track and bill my time.

If I have clients with ongoing needs - I just track time and bill them when I hit an hour.