Easy. Are you arriving at Malpensa (MXP)? If so, take the Malpensa Express to Milano Centrale (you can buy your ME and Milano-Padova tickets at the same time), then find the train to Venezia Santa Lucia (final destination). Padova is a couple of stops before Venice. No train changes after Milano, travel time is about two hours, trains leave every hour or less.
You can also take a train from Milano to Bologna and change trains there to get to Padova (train direction is still Venezia Santa Lucia), but the Bologna station is multi-level and you need to be alert to signage - plus schlep your luggage off and on an extra time.
Don't have a B&B recommendation but I have stayed at Hotel M14, near Prato delle Valle. Very good hotel, will loan or rent you bikes.