While I don't want to encourage anyone to freak out over one article, I have to agree with the writer on the juice issue. Juice is not a bad thing, especially 100% juice with no added sugar, but it's not necessary to drink it all the time. And even if it's all natural, it's still a lot of sugar. Better to have your son drink lots of water during the day, and a little juice with a snack once or maybe twice a day. It sounds like he's healthy now, but it's also important to create good habits for later. If he always drinks sweet drinks - even watered down juice - then as an adult he'll always be reaching for sweet drinks. And you won't be there to water them down for him. Get him used to drinking water, and that'll be a good habit as he gets older.
If he's resistant at first, then make the water special. Put ice in it, get a special sippy cup or a cup with a straw, maybe a crazy curly straw. (Another good thing is that water is not so bad to clean up and won't stain if it gets spilled!) My guess is, though, that if he's that active and thirsty, he'll drink whatever you give him.
I would also be careful about how and when you give him milk. It's nice to have it just before bed, it calms you down, but hopefully you're brushing his teeth! Milk has a lot of sugar in it, so it's not good to have it just before going to sleep if you don't brush. And if he's only getting milk twice a day, he should be eating plenty of yogurt, cheese, or leafy green vegetables with lots of calcium.
Sorry if this seems like a lecture, but good eating habits are so important!!