It's the bridges that are the main issue on arrival and departure day for most travelers. A slightly longer walk can be well worth it if it cuts the number of bridges you need to climb up and over. In this case, the Palazzina Veneziana is one bridge from the train station and the Ferrovia vaporetto stop. In fact, it looks as if it's right at the eastern end of the aforementioned bridge, the Pointe delle Guglie.
Option 1:
If you arrive by bus at Piazzale Roma, proceeding on food will also require you to cross the large bridge between Piazzale Roma and the train station, the Ponte della Constituzione. Most of the latter has shallow (half-height?) steps, so it's possible to roll bags up and down, with care. This is not a complicated walking route; it's on the way to the Rialto area and San Marco, so once you cross the big bridge to the area around the train station, just follow the mob.
Option 2:
Alternatively, you can hop on the #1 vaporetto at Piazzale Roma Dock G (according to Google Maps) and ride to San Marcuola, which will allow you to avoid both of the bridges that would otherwise be required. The walk from San Marcuola to your hotel is short (Google says 5 minutes) but does involve some turns, so I recommend having an electronic map on your smartphone and hoping you retain reception during the walk. You'll be going straight up (N) on San Marcuola, then turning left (W) on Rio Tera Drio la Chiesa, then right (N) on Rio Tera del Cristo, then left (W) on Rio Tera San Leonardo. After walking for some time along that busy street, you'll come to your hotel on the left just before you hit the bridge. I don't know how visible the hotel is from the main drag, Rio Tera San Leonardo; there's a street cutting off to the left, and the entrance could be on it instead. If you get turned around along the way, ask for directions to the train station (Ferrovia, "fer ro VEE ah"), because everyone can help with that (there might even be "Per Ferrovia" signs at intersections), and your hotel will be on the way to the train station from the San Marcuola stop. This would be easier than I'm making it sound.
A single vaporetto ticket costs 9.50 euros, so figure out how much you'll be using the vaporetti to see whether you'd be better off buying a 24-hour (25 euro), 48-hour (35 euro), 72-hour (45 euro) or 168-hour (65 euro) pass rather than a $$$ single ticket. Don't forget to validate the pass/ticket before each usage. You should see a green light on the validating device.
Option 2B:
Take Vaporetto 3 from Piazzale Roma to the Guglie stop and follow directions below for using the Alilaguna to Guglie.
Option 3:
Take Alilaguna Line A from the airport to the Guglie stop, as the hotel suggested. Walk to the right as close to the waterfront as you can. When you see a bridge to your right, you are there. Your hotel should be pretty much in front of you (not across the bridge). I'm not sure where the entry is. Unless Google Maps is lying to me, your hotel is not right at the Guglie stop. It is, however, a very short and easy walk from that stop. Just remember to head to the right when you disembark.
I see that Google Maps suggests taking Alilaguna A to the Madonna dell' Orto stop instead. It's a quicker trip from the airport but leaves you three bridges from your hotel (or four if you don't take the optimal walking route). I don't see any reason to do that rather than staying on the Alilaguna until it gets to Guglie.
I have never set foot on an Alilaguna boat, but I assume there's good signage from the airport. I wouldn't worry about getting lost on the way to the Alilaguna dock. (I'd pass because of the cost; I'm stubborn that way.)
