Just bring some crispy bills and get it at the blue rate to have some cash, otherwise use a CC which have a similar rate to the blue rate, and even was higher in the last couple of days.

Sending money in batches will be more expensive, because is only $8 dollars if you do it at the store and free the first time (online with a Debit card or Bank account), otherwise will cost you $15~20 dollar every time you send money.

If you have some pesos left, don't worry, the same place where you bough it (cuevas) will buy those pesos back, usually 20~50 pesos less than the buying rate. In the past I used Mais Brazucas (https://cambio.maisbrazucas.com.br), you can check their rates, is a travel agency located on Florida Street.