You can do a day trip to Venice but you'd miss out on the best part - evenings are the highlight. Venice is best seen at leisure and one day will not be worth the trouble - too much to see and do. There's a lot less in Milan and it can easily be done in a day - same with Como, which is very close on the train. The Centrale Stazione in Milan is not particularly close to many hotels as the area is isolated from the interesting parts of Milan. The NH Milano Touring is a nice place, about twenty minutes on foot or a two minute Metro ride - cab is only 5 euros. The ride to Venice (not Mestre) on a Eurostar City train (reserve a day ahead to get a discount) is pretty quick (see www.trenitalia.com) - to save money use the regionales - almost as fast and just as comfortable. It's easy to change trains at Centrale and go right to Venice and spend the night there. Bid 4* on Priceline - about $110 when we did it. That got a room right on the Grand Canal. You should plan on getting to a hotel by using a vaporetto. And spend a few days - walk around and take some boat trips. Buy a vaporetto pass.