The awesome thing about using an old tee is that you can also use the original hem for the bottom of the shirt and the sleeves. Yay for shortcuts!
Overall, it was an easy pattern to sew. The fit is slightly longer and thinner than most toddler T's. It works out perfectly for my tall, skinny boy.
The result is fabulous, minus my mistake of putting the pocket on the wrong side. I'm choosing to ignore that minor flaw.