After doing some more thinking on it I'm not completely sure if I should make an archive. Pruning threads automatically seems to keep in line with the general philosophy of most anonymous discussion board. Instead of archiving threads I could just increase the active thread limit from 15 to 20.
Can always test that out and keep it for the time being if that's what you'd prefer. That's fine with me. Maybe increase it overtime once the board becomes more active?
Why so few threads? Other boards keep tens if not hundreds of them. It's better for a slow site to have a lot of threads. If there's nothing new to talk about or if new threads aren't interesting you could always return to the old ones. Keeping few threads also discourages putting in effort. I made some large posts in the past but it's all gone forever now.
Okay it's been increased to 50 from 30.
I think it’s fine as is. In the end, this should still feel like a personal site’s guestbook.