If he doesn't sleep when out and he has NWs you know it's probably OT from not sleeping and you'll need to try to fix it the following day. So that isn't a mystery for you at least hehe.
The other nights though...I wonder if you try to keep your wake time and naps consistent if it would help you. So try keeping the first nap to only 2 hours at most. If you hit 2 hours you can wake him. Then the next nap should happen at the same time everyday in the pm b/c you'll know how much A time he needs between. If he sleeps longer than the 2 hours in the am two things might happen. 1. He won't be tired enough for your pm nap, and might refuse it or take longer to settle and then end up OT and restless which can mess up your nights. 2. He might make up for lost night sleep so much that he continues to wake often at night and make up for it with the long am nap.
Does that make sense? I think if you work on keeping that first nap consistent it might help make your nights a bit more consistent. Also for your own sanity, since he is waking with no pattern at night....maybe you can make a pattern. If he is taking a full feed when offered...try only offering a full feed at the same time(s) each night. So if you can handle 2 and 5 or just the DF and 3 or whatever then only offer feeds then. The other times keep comforting and resettling and teaching independent sleep skills and hopefully a pattern will emerge. Once he is only taking feeds at consistent times you can work on eliminating them, but it might help him establish a more regular sleeping pattern right now.
Lastly, he is getting a lot of daytime sleep if he naps the full amount listed in your day 5.5 hrs or more. He also may be showing UT signs by waking at night....esp. if he has been waking earlier than normal in the morning. If you aimed for 5 hrs or less you might see some improvement as well. 2 hrs. am 2 hrs. pm and a 30-45 min. catnap early evening.
I hope I haven't confused you. Let me know if you have any questions. Here is info on typical amounts of day and night sleep:
http://babywhispererforums.com/index.php?topic=85130.0Hope that helps you as well.