At first, I started out with a keyboard. Upright or grand pianos are extremely expensive, and if he has no interest in music, he wouldn't use it, therefore it'll be a waste. I started with a keyboard, and when I realized that I was serious about it, I got a piano about 1.5 years later. Now I've been playing piano for almost 7 years (7 year mark in January!, I'm 13 now), and a piano is definitely better than a keyboard- a keyboard doesn't have all 88 keys on it, and the quality compared to a piano is worse. So start with a keyboard.
As for classes, you can choose to get him private or public, although private is better than public. There are also stuff like you can learn online, or if someone knows piano, they can teach him, therefore not requiring a teacher.
You would want a metronome, as it will help your son to keep a constant beat while he plays. Let him play around with it to get the hang of it.
Good luck, and the most important thing is, your son having fun while he plays.
