Oh, my gosh - at THREE, he will probably not remember a whole lot of details about his birthday party, so I recommend keeping it as simple as possible. For my daughter's 3 party, we went to a park, asked four friends to bring a picnic pot luck item, decorated with balloons, & pinata. The kids played, we ate, did the pinata, and had cupcakes. After the party, she said "mommy I LOVED my party because I had blue icing on my cupcake!!" Ahhhhh, youth!!
With that said, I know you are not doing outdoors, so just don't spend a fortune, dress it up with some balloons, have cake & ice cream and let the kids run wild. I think a skating rink is a great idea. A friend of mine just took 4 friends out for pizza & a movie for her son's Dec 27th 3 year old birthday party and it was a big hit. In 5 years, you will be taking the whole neighborhood to Disneyland, so enjoy this time of innocence and don't over-do it!!