Mandello is a lovely place to stay regardless of Guzzi, have breakfast in Gelateria Costantin to start your day.
at the italian anima guzzista forum we are quite a few "on the ground" with many members living near Mandello, regretfully, no museum visits or tours until the reopening in september 26'
quite a few moto guzzi businesses around if you are in need of parts
no shortage of other moto museums in the larger area, like MV Agusta, Frera, Scooter/Lambretta Museum but youd need a car to go there.