For those who are interested.
I am planning to, at the end of each day, go through any topics that have not received a reply for more than 7 days, and all closed topics, and remove all uploads.
This will leave only text which can stay forever.
This should keep the site viable for a very long time.
This is the best solution until I can get a permanent delete that will delete entire topics.
The added benefit of not deleting entire topics is that text and history can remain in the database theoretically forever, to be viewed as anyone sees fit.