Your son seems to be ready to transition to one nap a day. I'd try to put him down 30 mins later for his first nap and if this one lasts less than 2 hours, then try a catnap in the stroller/car or even quiet time in his crib for the evening. Then you can try an earlier bedtime, even at 645, so he can catch up for the naps he's missing.
IF you have trouble keeping him awake for longer stretches, you can introduce healthy snacks at the used naptimes to help him hold on for longer. That should also help with his eating at lunch and dinner, since he'll get more calories in, as they get into toddlerhood, they need to eat in shorter intervals instead of big meals.
Try the new adjustments for a week and see how they work. It's a long (and sometimes tough) transition that is only figured out after lots of tweakings so be sure to keep us posted to help you throughout. HTH!