Congratulations on booking one of the best small hotels in Zurich Canton. : )
I'm biased, because Hotel Sonne is less than 10mins walk from where I live, and I walk past it every time I go shopping in the village. In the height of summer and winter, Hotel Sonne is the hub of village activity due to the lake front beer garden, which is transformed into an ice rink in Winter.
You're also only a couple of minutes walk from Kusnacht ZH train station via an underpass at the side of the hotel, giving you direct access into the city centre every 15mins. It only takes 10mins to Zurich Stadelhofen (my preferred station) and 13mins to Zurich HB. You also have branches of Coop, Migros and Avec supermarkets in the village centre, plus a small number of bars and restaurants.
Küsnacht is a village in it's own right, rather than a suburb of Zurich, with a pretty village centre, and is on the Gold Coast, so benefits from views of the opposite coast lit up by the morning light, and glorious sunsets over the lake, whilst the opposite Silver Coast, is in near darkness. We very deliberately chose to live in Kusnacht for the quality of light.
If you decide to visit the Lindt Museum, the Kusnacht boat jetty is directly next to the hotel, where you can catch the 'short lake cruise' at 00:28 mins past the hour, arriving in Kilchberg at 00:02 past the hour. You get great views down the lake to the mountains as the boat crosses from Erlenbach to Thalwil.
https://www.zsg.ch/en/timetable-prices/timetable-assistant/round-trips-scheduled-cruises
When you arrive, I strongly recommend you take a stroll along the lake front path, which runs from Seebad Kusen, past the lifeboat station, around Kusnacht Horn, and along Hornweg to Zehntrotte, where you'll find the old boat house, which dates from around 1290. From there, walk up to the main road, Seestrasse, and you'll find Rico's, the Michelin Star restaurant once favoured by Tina Turner, who lived a couple of doors down, at Algonquin. You'll also see that us locals gather on the lakeside in good weather to swim, paddleboard, and picnic, so bring your swimwear.