C.P.
I have had two very different experiences. My first went to one nap at 12 months. My second is 18 months and is still taking two naps. If we have an activity, he will power through in the morning, but if not, he usually gets very tired and needs to go down. I want him to be done, but you can't force it if they aren't ready. So far, it's been a pretty natural transition for both boys.
One thought on your recent experience. A 4:00 nap is very late. He may very well have been overtired by then, which all the experts say means he is going to have a very hard time napping. With my 18 month old, I am waking him after 45 minutes to an hour in the morning so he will continue to have a good afternoon nap. Perhaps you should let Milo have a short morning nap and then make sure his afternoon nap is earlier - I'd say no later than two. I wish I could remember the name of the book I read that really helped, but I can't. It talked about naps, transitions, and natural sleep cycles.
Good luck!