If you have an exhaust fan already I would consider replacing the switch controlled unit to one that has a humidistat built in so it can turn itself on and off as needed. I ordered one from home depot and installed it for my basement build. I would also see about getting that mold tested and mitigated as some types of mold can pose a significant health risk. Once the mold is mitigated you should consider sealing the space with plastic to trap the humidity in that space and allow the exhaust fan to push it outside instead of allowing it to absorb into the walls and ceiling which will allow an ideal environment for mold. Good luck on resolving the mold issue.