Aunt-Leahs
There is a table called ost_form_entry that I cannot seem to find any sort of documentation as to what that really holds and whether it can be safely cleaned or not? I've seen some posts that suggest it and others don't mention it at all.
I wouldn't suggest blindly truncating this table nor the _form_entry_values table. Some of these records relate to Users, Organizations, etc. So you'll need to match them to objects you want to actually delete like Tickets, Tasks, etc. We don't have any guides on this so you'll be on your own; proceed at your own risk and be SUPER careful. Take backups before just in case.
Are there any other tables that I missed below, in order to make sure that all stats, attachments, etc are also removed?
Yes, you missed a few. You can review the Database ERDs here. Be super careful deleting the _file_chunk records as some of them might be related to system logos, images used in email templates/signatures, etc. Again, it's best to relate them to the necessary objects you are attempting to clear.
Do I need to reset any auto-increments back to 1 or does that automatically happen when i use the DELETE FROM statement?
If you truly want to start over that'd be best however if done incorrectly and on the wrong tables, etc. it will have detrimental impacts later on or even soon-ish.
In summary, I would not recommend embarking on this unless you are comfortable with databases in general and can understand how all the tables relate to each other and how to relate records in some tables to needed objects. If you are uncomfortable in the slightest I would instead recommend installing a fresh instance and simply importing Users, etc. and recreating any Help Topics, Agents, Departments, etc. This would ensure the safest path forward.
Cheers.
