Naps

When she can manage 4h for the first WT, then she's down to a 4/6 schedule. Shift bedtime earlier if she has early morning waking. With brain maturity, she will eventually let you know when she's ready for a 5/5 schedule (when you see an undertired nap that is between 40-55m long), and gradually a first WT that stays at 6h for quite a long while.

It really depends on your toddler. Some toddler requires two nap. But you can try to see signs of them cutting down their nap. Unable to sleep on their first nap timing but able to sleep at their second nap timing. Or Longer first nap timing and skipping second nap for a few times

Depends on your toddler and what the routine is. I'll let my child sleepif it's much needed. Now that he is 3 heonly has 1 nap a day.