I haven't been to Universal/IOA since November of 2013, so no tips about going in the Summer with some newer things opened. (We went in the off-season).
However, we have taken young children. (My second child's first trip was at 2 months. The third child's wasn't until 11 months). I was nursing my kids so that made it easy. I just nursed wherever we were and gave them tastes of food from my plate once they were eating. None of mine were that into food at 15 months - but if yours is, take some familiar food into the parks for your child. Also, there are times when a kid needs food ASAP and waiting in line for something can take way too long to a baby or young child so it's best to have something easily available. The website says you aren't supposed to bring in food and drinks, but I've never had any issues with this. (I don't take in an entire picnic lunch, but have always taken in several snacks for the kids). I found a carrier, like a sling, to work wonderfully with my kids when they were young. It was so much easier to stand in lines or walk in crowds. I would also take a stroller though - especially if you have a baby who can only lie down for naps. A stroller with full recline is great. With one of my kids, I would then take the sling off and put it over the stroller to block out the sights and make it better for napping. (Other two refused to sleep in the stroller at all). Also keep in mind that nap refusal can happen taking in all the sights. That happened with my 11 month old on his trip - he didn't fall asleep for his nap until 6pm the first day! (And only while in the sling).
Use baby swap whenever possible for rides. (I can't remember if it's called rider swap or what the official name of it is at Universal). For most of the Universal rides, this meant we stood in line together and then the parent with the young child would go wait in a room instead the ride and then swap off when the first person was done. So - waiting in line just once and you get to wait with each other. We actually prefer this to how Disney does it because it meant we stayed together and the kids not riding got to see all the cool stuff in the lines as well.
As for what to areas to focus on for baby, I wouldn't worry too much about that. I would focus on baby to know if he's too hot, too hungry, too overstimulated, etc, but get in the rides that you and your wife want to do. Babies don't care that much. If you think he might like to see characters, then see if they still do the storytime. They used to do that at the Circus lunch place. (Circus McGerkus?) There were lots of characters during that and no lines - and air conditioning! My kids were never much into characters so we didn't work hard to get them in, but that place was one of the few exceptions to our character greeting. (Though it may have been for me as much as for them . . . )
