Water taxis Venice: detailed information, pre-orders and prices. Water taxi or water bus in Venice? Difference, advantages and disadvantages of the two modes of transport.

This explains the difference between a vaporetto and a water taxi. In a way, it is a little bit like the difference between a bus or subway in a city and a private taxi. However, I find a vaporetto easier to access than a bus, and of course, much easier than elevators and stairs to subways. With the vaporetto, you have just a dock.
We have never needed or taken a water taxi in Venice, though with a group, it would be a nice way to arrive in Venice from the airport.
You will be both arriving and departing by train, so a vaporetto should be just fine. BTW, arriving by train and stepping out to the sight of the Grand Canal is, IMHO, one of the most wonderful experiences in Europe. Take a moment to savor it when you arrive at Santa Lucia Station.

I agree Sassafrass that if you are arriving in a group from the Airport a water taxi can be a good option but isn't necessary or even desirable going to and from the station.

<<You will be both arriving and departing by train, so a vaporetto should be just fine. BTW, arriving by train and stepping out to the sight of the Grand Canal is, IMHO, one of the most wonderful experiences in Europe. Take a moment to savor it when you arrive at Santa Lucia Station.>>

This reminds me of the first time I took the train into Venice and not sure of where to get off just followed everyone else off the train. Imagine my surprise when I exited the station and looked for the Grand Canal only to see it wasn't there. Turned out I'd got off too early and I was only at Mestre. Ah well. Unfortunately it turned out that at Mestre you have to negotiate a tunnel between the concourse and the platforms, so as I had a heavy case I had to go back down in one lift, decide which train to Venice I wanted to catch, take the left up to the platform then wait for it to come in. I was very happy when I finally exited Santa Lucia to see the Grand Canal in front of me.

Not as hard as you think. Our first multi city trip we took 2 large suitcases and a carry on (backpacks only since) and we walked from hotel to where the boat is that takes us to the train station.

My only advice is to stay in a hotel that is close to the boat (that was blind luck for us). Worst case is you carry them for 10 minutes, not a big deal. Once you get on the boat, it is comfortable and they drop you off right by the train station.

I would not however force myself to choose a hotel purely due to proximity to the boat if you don't like location.