As I do not know anything about the forum crash here is a basic explanation from the Tech who got it up and running again.
The cause of the problem, as was the problem last time. Is that the code that runs the forum is not matched to the system running it. This is generating some errors, these errors are recorded in your database (probably 10x per page view). This looks to be the cause of the space problems you are having.
Other factors can contribute as your forum grows, like hosting pictures and new accounts; but once the code problems are fixed you will be able to better assess your needs.