For your arrival into Marco Polo Airport you have a few options. You can take the bus or a taxi from the airport to Piazzale Roma and then take the Vaporetto. The closest Vaporetto stop is the San Marco terminal and you want Line 1 or 2. It looks to be about a ten minute walk from the terminal to Hotel Monte Carlo.
You can also take take the Alilaguna water bus directly from the airport to the San Marco terminal. The Alilaguna boats take about an hour and leave every 30 minutes from the airport.
When you leave the easiest way to get to the San Lucia Train Station would be to take the Vaporetto from San Marco to the train station. Again, Line 1or 2 would get you to the train station and they leave early enough to get you there in time for your 8:20 am train. Although Hotel Monte Carlo is closer to the San Marco terminal it looks to be not that much farther to the Rialto terminal. The only issue with walking from the Rialto stop is that many people use this stop so it is always very crowded and it’s easy to get lost without specific walking directions.