You can get across the lake by boat or around it by taxi. If you plan to mostly stay at the hotel and visit one other town like Bellagio, you don't need the car. If you prefer to explore many towns along the lake, you should keep the car.
Milano to Como is quiet an easy train ride but Moltrasio is approx 10 km away from the Como station. We chose a taxi but another option is to walk to the waterfront and catch a ferry to Moltrasio, but you would need to be prepared for a slower journey and the walking