This is your first time in Italy and if I recall correctly, you're travelling alone? The optional excursions are listed on the Globus website. Not all of them will be made available to your particular tour group. Your tour director will give you a list of the ones being offered to you and will take time to tell the group about each of the different offerings.
From what's listed on the website, I'd advise you to budget for all of them. You're not going to want to miss out on any opportunities. Whether or not you decide to take all the optionals, it would be a shame to make the decision solely for money reasons. The meal optionals are often a disappointment - foodwise - but they are located at unusual venues and often include entertainment. And, the tour group almost always has a very good time together especially since for these dinners the wine flows and people are "in good spirits". .
Your hotel at Venice will not be in Venice proper but on the mainland (Mestre), outside the city. The advantage of the night out optional is it provides you with transportation into Venice and back to the hotel. If you really have your mind set on doing Venice on your own, I'd advise you to have a discussion with your tour director about getting there and back from your hotel.
The tour brochure refers to the optional excursion to Burano. You might want to check out some tour books about Italy and Venice because Burano and Murano are both on the waterbus route. People who want to do Venice independently often choose to take the bus out there on their own - if there are enough hours allocated for that. However, I've heard positive comments about the Burano lunch optional if you choose to let the tour company do the work for you and be less adventurous on your first trip. That's the beauty of coach touring.. .. .
Once you're on the tour, you may want to chat with other tour members to discuss what they are signing up for and why. Sometimes, rather than go out for the group dinner, couples and individual tour members get together to go out at a local restaurant.
Finally, if you haven't already checked it, I recommend looking at the Trafalgar Tours website. (
www.trafalgar.com > message boards) Whether you're travelling with them or another company, this is a very active website with lots of good input from the members. You can use the search (Find) feature to look for specific information.