Hello, Alex,
Short answer: Don’t invest in the sport.
Longer answer: 20 kts plus: infrequent. Mainly during winter and spring, but sometimes in summer. Note: it’s been a shocking year for wind this year.
Side on: look for SW'erlies blowing on shore between Safety Beach through to St. Kilda.

Westerlies occasionally.
Side: hardly ever.
Sail size range: 4 to 5. A 5.0 will work in 20 kts and a 4.5 will cover MOST of the winds above 20 kts.
One board: 82-85 L waveboard or something like a Tabou 3S, single fin. Get a number of wave fins, from 27cm down to 20 cm, to extend the range of the board.
Where: Safety Beach, Frankston, Keast Park, Bon Beach, Parkdale, Mentone, Rickett’s Point North, Hampton, Dendy Street, Elwood, St. Kilda, Middle Park.
How Often: never often enough.
2 Hour road trip: Torquay or Westernport fit the bill.
Once a month on average: 12 times a year is possible, but generally forget the period March to about the 2nd week of June (Autumn = the doldrums

).
Hawaii: let’s see. Warm water, great swell, great winds, girl sailors in bikinis. Have to say H is the place.