I like doing different things so I hope some of this is helpful, or at least an interesting read for you.
Can this app send messages and files to offline recipients like Bopup IM does? Is there a way to keep and review conversations for all users in the system?
I don't think you can with this program. It's only meant to communicate within a lan and not necessarily an IM app. To be honest I didn't try messaging while one of the users was offline, so I can't really say, but my guess is a no on that just because of what the program is.