regarding your last question, especially if you stick with the Murano idea.
Taking an early flight from Venice is a perennial bugbear here on the Forums, and I can remember that it has always been a bugbear over the nearly 20 years I've been active here...
The problems are two. Venice - except for the industrial areas of Mestre and Maghera on the mainland - is a collection of islands, and Murano is an isolated island, so boats or bridges become critical to get to the airport which is on the mainland northwest of the islands. The other problem is that early flights at the airport are really truly early.
Oh, and there are no hotels at the airport, some nearby but none on the airport.
Boats don't move very fast. Scenic (if your eyes are open after getting up at 2 or 3 in the morning), but goodness it will be early.
If you were on the main islands, in one of the six regions of Venice, your choices are a lot more than if on a remote island like Murano. On the main islands, you can make your way, no matter how early, on foot or by Night Vaporetto to Piazzale Roma where you can catch an inexpensive dedicated bus for the short trip over the causeway to the airport, or take a normal land taxi. Or you can take a private water taxi (€€€) from a hotel with a private dock to the airport, or an Alilaguna boat (by many miles not my favourite, I really dislike them) for the slow boat ride to the airport.
On Murano you can only get to the airport by boat. Conceivably you could take a daytime vaporetto to P.le Roma and do as above, but those daytime vaporettos to P.le Roma won't get you to the airport in time for an early flight.
Realistically, on Murano, you will be limited to private water taxi (€€€) or Alilaguna.
So your savings, if any, from staying on Murano and travelling to the main islands for everything, may well be eroded by the inconvenience and expense. Taking an easy bus from P.le Roma is only €5 or so plus your existing vaporetto pass.
Some of this might be easier and somewhat less expensive if you stay on Murano and take a later flight so you can take a daytime vaporetto to P.le Roma and then the bus.