When the OP post of a topic gets deleted (happens a lot when a qeustioned is answered for some reason), it makes the thread seem to start at a weird point, rendering it often a total useless topic.
So i would suggest you cant delete the opening post of a thread, without deleting the whole thread as well (which btw not anyone that made the thread should be able to jsut do, but instead maybe a button to “flag for deletion”, so the mods and devs get notified the OP want the thread to be deleted, and then it up to the mods to judge if it is fair to delete it.
Maybe the abbitly to delete a thread without say 3 hours or so after you created it without having to ask mods, could be fair in case you accidnetly double create due to lag or something)