You've got some really good advice here from different moms! The only thing I can maybe suggest is, can you wake him up earlier in the morning, like maybe 7 or 8 am? I know it would be hard to do so after he's been up so late the night before, but I know if my son slept until 10 am, he would be up until 11 pm too!
My son is 3.5 years old and has not taken naps since he was 2.5 years old. On the rare occassion that he does take a nap (like if he falls asleep in the car, or if I talk him into taking a nap for the sole purpose of staying up late (like on New Year's Eve), he will stay up until AT LEAST 11 pm, even if the nap lasts only 15 minutes. I know, I've had people (even nurses) tell me that at 15 minute nap should not affect my son's ability to fall asleep at night, but trust me, it does. If he's had any sort of nap that day, instead of going to bed at 8:30, he will be unable to fall asleep until 11 pm or so.
The same thing happens if he sleeps in late. He usually does not sleep in late, but just as there are rare occasions that he naps, there are rare occasions that he sleeps in late. On any given day, he is not ready to go to sleep until at least 12 or 13 hours after he has waken up in the morning; if he wakes up at 10 am, his body will not let him fall asleep until 10 or 11 pm that night, even if he is tired and even if he needs to catch up on sleep. It is a vicious cycle, and the only way I can break it is to wake him up early (like 7 or 8 am.) He will be tired, but then at least he will go to bed at a decent time that night and break the cycle.
Like I said, you've got a lot of great responses from other parents, I guess its all sort of trial and error for you to see what works best. I do agree with what I read that he may be acting up because he wants / needs your attention. New baby or not, if a child wants your attention, they will do anything to get it, even if that attention you are giving him is negative (discipline; he thinks, "Hey, who cares if she's yelling at me: At least she is paying attention to me!")
You can also try giving him a variety of different activities to do (like playdough, coloring, puzzles, etc), and you can try rotating his toys so they seem new and exciting to him after a while. We have so many toys at our house, I keep most of them in storage boxes either in the kids closets or the basement, and then every week or two, I box up the current toys and put them away while bringing out a different box. Boy, you'd think it was Christmas again!
I wish you luck!