Fast answer
A strong Varenna-local day starts with Villa Monastero, then adds only what the calendar, tickets, weather, and walking plan can support. Villa Cipressi can be a good garden pairing when the day has enough time, but it should not be treated as automatic. Vezio is a separate hill route, not a quick extra after two gardens. The Greenway works best as a local walking fallback when ferry movement or hill timing would make the day too tight.
If you only do one thing
Start with Villa Monastero as the fixed calendar check, then decide between Villa Cipressi, Vezio, or a Greenway-style local walk. Do not stack all three unless opening days, ticket windows, last admission, walking route, weather, heat, and return timing still leave real slack.