Free space isn't relevant since autogrow is what happens when the free space runs out. It doesn't force any space to be used. 1% is probably rather low, but in any case it's usually best to use a fixed number of MB instead of a percentage (maybe 500 to 1000 given the size of your database). sp_spaceused is a good place to start for monitoring. There are more sophisticated techniques, which you should be able to read about on the internet.

John