It sounds like he is definately ready for one nap. the second nap is late in the day so possibly that is why it is a struggle for him to sleep then, and when he only has one nap, he must be overtired, Harrison is a nightmare to get to sleep when he is overtired and I have to place my hand on his back to help him settle.
With a 5am wake-up ( and I have been there lots!) I would put him down for a couple of days early, say 8.30am, but for a catnap only. 30 mins - 40 mins at most. Then with a bit of luck you should be able to get a lunch time nap in, 12.30ish, which will tide him over until bedtime.
I tend to go for a bedtime - 4.5 - 5 hours after wake-up from nap, earlier if they seem tired. The early bedtimes are essential when transitioning to one nap, as it is the overtiredness that causes night-wakings and early mornings in transitions! Once he has caught up with his sleep, you may find he sleeps in later and you should be able to drop the cat-nap. Give a snack at naptime to tide him over and plenty of distraction, and then you will probably need to shuffle the one nap and bedtimes about until you get to the desired point!
It can take several weeks for them to adjust, so hang in there.
With the problems at bedtime, once he is rested, you may find he settles ok, otherwise, I personally found a gradual withdrawal worked. I sat at the end of the cot, no eye contact etc, laid him down when he got up, completely emotionless otherwise it becomes a game! I would read a book until he settled to sleep. He still jumps up and down now, but it takes him 10 mins to settle like this, then 10 mins later he is asleep, so I don't stress about it so much. It's like he just needs reassurance I'm around.
Anyway, hope some of this helps, sorry for waffle, harrison is climbing on my lap trying to push buttons! LOL!
Justine