I agree with Peter's (Carmen) suggestions completely.
For question#2,I want to tell you that I've been in Burano last September
after maybe 16 years, and I was stunned at the number of tourists cramming
the narrow streets. Definitely, I would go there only on a winter weekday
morning, although it is(it used to be) a really magic place.
If you choose to go, I'd go by vaporetto. It's cheap and funny, and usually
you can find seating place if you wake up early. You can easily combine
Burano with Torcello.
But, all in all, for your only day in Venice, stay in town.