I use the 12x9 int3, but I have been considering a smaller model for a while now, just haven't gotten around to actually buying it, I do love the large one, but I think that now I could go for a smaller one to save some space on my desk, and to have more mobility.  I like to make large brush strokes and when I was researching this back in 2006 I read a lot of people who said it depends on your brush stoke, so I went large, but for the work I do now, I think small would be better, so yes its VERY true that bigger is not always better, it really depends on  you, your style of painting and work, and your space.

It took me 1 painting to get used to it, I switched back and forth a bit, but eventually stopped.  I do still use the mouse for some things that are easier for me with the mouse, like the busy work of doing clothing textures, but even there I will switch to the pen for detail.

The pen pressure is amazing, and makes all the difference in the world as far as painting goes =)

Good luck and congrats, you will love it!