How do I refinish a bathroom ceiling after it got moldy and peeled?
Paint may have helped.  It would act as a bit of a seal, causing the water to drip off rather than absorb into the texture.
I would do it smooth.  A rough surface has a larger surface area meaning a larger surface for condensation.
I would recommend against texturing at a later date.
I would put a fan in.  It's a good idea to put it on a timer so that it turns off automatically.  This allows you to leave it running after you leave, and is also good for bathroom odors.  Also, be aware that cheap = loud when talking about fans.
Definitely put the fan in before. You're going to need to cut and repair drywall as well as drill through the brick to create a vent.  You'll mess up any work you've already done.