# of posts per screen, different for each forum
 

Is there any way to change the # of posts that are displayed per screen for different forums or do I have to use the same # for all forums?

Some of my forums are picture-oriented, so I only want 5 posts shown per page since each post can be very long. But in my discussion-oriented forums, I'd like to have 10 or 20 posts shown per screen.

Is this possible?

Not out of the box... sounds like something that could be handled by a mod but I don't know of any such one to do what you want... You could request one in one of the requests forums, either paid or unpaid.