Venice Transport

I'd get a 7-day vaporetto pass for unlimited use, even though your stay will be shorter. This website may be outdated but it looks like the pass would pay for itself in just eight rides. You're likely to take many more.

Yes, I think a pass is a good idea. A 7-day pass is 65 EUR. Considering that a single trip is 9.50 EUR, this will pay for itself after 7 trips. You can purchase them outside S. Lucia station at the ticket booth.

I count a minimum of eight rides, so that weekly pass is the way to go.

7 times 9.50 equals 66.50, but I didn't take the new math.

I barely passed the old math, and I think this website has current fares, vs. the one I linked to above. It also has a lot of other good info about Venice. The current single-ride fare is 9.50 for us visitors, and 65 for a 7-day pass. So the payback is on the seventh ride and the rest are free. The OP's plan involves at least eight rides just onto and off of Murano, and probably more to see the whole Grand Canal, other islands, etc.

Walking is indeed the best way to get around Venice, the only way to get to many places, but the vaporetto is great for covering more "ground," resting your feet, etc. It's fun but can be confusing. At least twice I boarded one going the wrong direction and had to get off at the next stop to turn around. The pass turned an expensive mistake into an amusing experience.

Staying on one of the off-islands (Murano, Giudecca, Lido, etc.) for more than one night basically requires purchase of a vaporetto pass for the duration of the visit. The fringe benefit is that with the pass in hand, you can opt to use a quick vaporetto ride to cross the Grand Canal if you're nowhere near a bridge or an active traghetto crossing.