Shorten his naps by an hour or so to see if he's able to go to sleep at his regular bedtime. 2 hours should be the max at this age, otherwise it really interferes with night sleep. Most toddlers sleep 10-13 hours a day, so if he's sleeping 3 hours or more during naps, the most you can realistically expect him to sleep at night is not quite 10 hours, and waking between 5 and 6 am.
Toddlers need a bedtime routine from 15 to 30 minutes long to help them relax and get ready for sleep, so start around 7 and include calming activities such as a bath, reading a story, and listening to soft music. Then no lounging and talking and playing, it's lights out and bedtime. Don't allow the routine to become too long or too complicated. Allow your son to make bedtime choices within the routine like which pajamas to wear, which stuffed animal to take to bed, what music to play. This gives him a sense of control over the routine so he's a part of it and more apt to follow through.
As far as the higher-pitched voice pay close attention to what he's watching on TV, and those he hears talking around him. It sounds as if he's imitating someone. I was wondering where my guy, who's 26 months, was picking up a distinctive way of talking (not bad) and realized he's talking like Caillou on Sprout.