Forum Moderators: rogerd
Marsh
You won't have to learn PHP unless you want to "hack" your forum software, and even then you can probably accomplish what you need to without becoming a skilled PHP programmer. The popular package have many hacks that can be installed with minimal programming knowledge.
As far as time needed, you can probably get a forum up and running in a few hours if you don't do much customization. Ongoing time needs will be low at first (when there is little activity) but will increase if the forum gets busy. One thing you can do to help the workload situation is to recruit volunteer mods if the work really ratchets upwards.
In the early days, consider putting yourself on e-mail notification for new topics - this will let you spot spammers in a hurry, plus allow you to get new posters a prompt reply.
Good luck!