Wayne,
First, welcome to Bonsaitalk, second take a minute to enter your zone information so others might be able to give you more specific information.
Here's a link to some information on this species.
Mountain Ash or Rowan
I would recommend watering the tree only when it needs it. Check the soil with your finger if necessary. After a while you will become more aware of how much the tree consumes.
This tree is naturally frost-resistant so I would think moving the tree inside and back out would be more stressful then simply leaving outside.
I love this species of tree but have yet been able to acquire the right one.
Good luck, keep us posted on your progress.
Green with envy,
Patrick