Help from Buenos Aires, Argentina

[Wetdoc]

Nemo,
If your limit is 11, then start from Rio in early April may not be enough.
Discounting you leave Angra and not Rio, has a half-day sail to Ilhabela, national capital of sailing. Another half day to Santos, but that does not offer much tourist interest to you.
I would go from Ilhabela to Sao Francisco do Sul, about two days, since SF has a nautical museum highly recommended.
From there to Florianópolis ( Floripa ). You can navigate from Florianopolis to Buenos Aires, but there are two problems. Florianópolis is not egress port, so you must take a bus to Itajai, about 2 hour, and complete the formalities there.
The other problem: Florianopolis to Rio Grande do Sul are 3 days at sea, but here begins the autumn winds, and begin to dominate the South wind, so it is usual to have to wait several days in Floripa on finding the correct window winds to make this leg. The most difficult part of the route from Rio to Buenos Aires, with almost no alternative on the way.
To pass between the island and the mainland in Floripa you must pass under a bridge, only mast up to 17 meters. Otherwise you should go off the island.
Rio Grande do Sul (RGDS) you probably have no interest, but that is easy to do all the paperwork, Receita only Monday through Friday, and early!!
Next port of La Paloma and Punta del Este ( small Monaco! ) in Uruguay, 30 to 40 hours of RGDS.
I think you must get to Floripa with a margin of days, to get out without the pressure of roles and formalities.
Wetdoc