Well, I've known this was going to happen soon and it finally did. Today we reached the 15GB disk space limit on our Gold level hosting account. That 15GB contains all the forum software files, database and user attachments such as uploaded photos and avatars, etc.
To keep things going, I've upgraded our hosting package to the Platinum level which doubles our disk space to 30GB at an additional immediate expense of $103 and a new annual hosting expense of $499.50 which will be due on June 1st, 2021. There are no additional expenses anticipated until that time.
It took us 10 years to use up the initial space so I'd anticipate no additional upgrades necessary for a very long time.