Actually 90MB is the default. They don't appear to have imposed a smaller limit than the default.
this isn't iOS, disk space and memory needed are two entirely different things.
Did the problem start with a WP or plugin update installation?
Testing on "your" server isn't the same thing as real-time performance. For starters your servers environment isn't exactly the same. For second, your probably not generating the same "load" during your testing as that's very difficult to do "offline". (random visits by users and pseudo-users or bots)
Can't tell you because I don't know what kind of "limited permissions" you have in the panel. If someone is granting limited permissions to a panel account there is MANY MANY check boxes.