>In those places is it possible to actually have a waterfront home, so you could keep your boat right there on the beach in front of your house?

You can. Prices go up as you approach the waterfront, but are lower then the US, for similar locations.
Buzios is the most expensive followed by Angra and Florianopolis. The Northeastern coast is a lot cheaper. Needless to say, prices depend on the exact location within the region.

An interesting fact: the Brazilian law establishes that all islands and all land 150 m from the high tide line are public property. "Waterfront property" does not assure exclusive access rights.

>If that is not an option, can you leave your boat on any of those beaches, mast up, and not worry about it being stolen or vandalized?

Depends on the specific beach we are talking about. As a rule, when you move away from the big cities/downtown things get safer.

> Are there sailing clubs or catamaran fleets in those areas where boats can be left permanently?

No catamaran fleets exist outside the main yacht clubs. Small sailing clubs are present in all this places, generally close to downtown and sometimes in less atractive - but sheltered - locations. Note that prices are not nearly comparable with the US. Also, there is no atitude or discrimination against multihullers. Actually, most clubs are small and new members are wellcome. (exceptions are the main three or four traditional clubs located in big cities like Rio - but those do not fit all the required conditions).

An interesting fact: in the northeast, fishermen (called "jangadeiros") have their home close to the sea and live their small sailboats in the beach. They are very easy going people and accept to take care of our "fancy toys" for a few bucks - even out of friendship, after it is established - but only if you are also nice.

The number of "Jangadas" in the area is estimated to be at least in the thousands, maybe tens of thousands - but no one knows for sure.

Cheers,
Luiz