You'll want to book your accommodations soon. Availability may already be getting limited. Definitely stay in Venice proper, not in Mestre on the mainland. The train station you want is Venezia Santa Lucia. We like to stay near the San Zaccaria (sp?) Vaporetto stop. It's close to San Marco, without being too close, if you know what I mean. Others may prefer other areas. It's not that big a place, so you really can't go wrong. But it's nice if you can find a place relatively close to one of the vaporetto stops, so you aren't schlepping luggage up and down endless bridges. I use booking.com to find potential hotels, then check reviews on TripAdvisor, and their location on Google Maps. We've stayed at a Hotel Campiello our last 2 times, and like it very much.
No need to pre book a gondola ride. If you see a gondolier parked, ask where his favorite route is. I'd recommend a route that is away from the Grand Canal. Just too much traffic there. If you want to ride up or down the Grand Canal, do it on a vaporetto. You can Google gondola stations to see where they cluster, but you can find them all over the place.