Yes & worth it.
Yes, although it's best to book the tour you want ahead, online or by phone but you can walk in& get general admission tours (the intro tour).
Yes. There's an entry down the stairs from the parking lot where you buy tickets from the house tour , museum and garden. Then you take the shuttle up to house and museum. Check out the gift shop. It's very nice.
Or get the package of the various museums and parks in the area. Longwood Gardens is beautiful and package is valid for the season.
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