hey fluffy,
1. your tree will do BEST outdoors in the spring and summer (trees are ment to grow outdoors). An open window would be your next best option...just make sure a gust of wind cant blow it off.
2. Water during the growing season means while there is active growth, ie spring, summer, early fall. DO NOT OVER-WATER YOUR TREES, as this can be worse than under watering...i know it is a daunting idea of when to water but there are a couple widely accepted techniques for telling. 1. Stick a WOODEN chopstick in the soil halfway between the rim of the pot and the trunk. Pull it out daily and check it it is wet, moist, or dry. You should water when moist. If you water when wet it will not allow the roots to recieve the oxygen they need to thrive. Dont ever let it get completely dry...thats bad. 2. The finger test. Stick your finger up the the first nuckle into the soil. Is it wet? Moist? Dry? Get the idea
In the late fall and winter months when trees are dormant they require rather little water. Your tree should be kept barley moist, but not allowed to dry out completely
Feeding (fertilizing) should be done with caution. Check this board for articles on feeding.
3. Feed your tree at 1/2 the recommended strength on the bottle. This will prevent OVER-fertilizing which can burn the roots. When it comes to feeding I go by the motto light, and often. Actually I use and love the slow release pellets. They kinda take the guess work out of feeding
I would recommed you get your hands on a good bonsai book...I recommed Bonsai techniques 1 and Bonsai Techniques 2, both by John Naka. Also, you may want to get some specifics on Holly...care sheets are availible in the "links" section of this website.
Good luck and happy bonsai-ing!
-Moe