I agree with the above answer. Our boat wasn’t full so we had plenty of space. The glass-blowing demo was the only ‘tour’. The other time on the islands was free time to explore, so you can escape crowds.

Our pick up was down a little from hotel danielli. At grand canal. Just down a bit from st marks square. It’s just a small kiosk. But you should check email ticket they sent you in case it changed

There are river buses going to both islands daily throughout the year so you can make your own way there for a lot less than an organised tour

The boat departs from a public dock/boarding area on the Grand Canal. The important fact is the meeting point however. Once everyone has gathered at the meeting point the guide will escort the group to the boarding area. The meeting point overlooks the Grand Canal and is a short walk from St. Mark's. The meeting point is a yellow booth with a white umbrella. On the side of the booth you'll see "Murano and Burano Tours". The tour begins at 11:30 am and the booth opens at 10:45 am.

I would think so. But safer to ask the tour operator