Hi!
I would aslo agree that the nightwakes could be because he is UT, ie not enough A time in the day between naps and too much day sleep. Although if high sleep needs 3hrs of day sleep may be ok just need to push that A time.
My DS was on 2 naps until around 19 months he was HSN, but he would go 3/3.5 hrs between naps. Wake 7 nap at 10 for an hour, nap at 2.30 til 4 then bed at 7! Slept sound at night.
On the other hand my DD was just about on one nap by 12 months. And we were definately capping and extending A at 11mo. I believe her day looked something like this- wake 6.30 nap 10 to 10.30, nap 1-3 and then bed at 7. If she had too much day sleep, her nights were effected big time.
As pp said, id try pushing that first nap out to be later. Abd see how you get on. It may be that you would then need to cap one of the naps anyway to fit them into the day.
Hth