Since you are not yet certain of which country you will eventually settle in, there is no point in getting an FBI report (required by migraciones to obtain a temporary resident visa) until you have made that decision as the report becomes invalid if you (even temporarily) return to the USA before the residencia pecaria is granted (when migraciones has accepted your documents and your temporary residency is pending).
I strongly urge you to bring documentation of the source of the funds which you will be accessing while in Argentina: A copy of the real estate contract (and/or any "official" document that shows the numbers!) if that's the source of the funds. Otherwise, xoom will ask for you two most recent pay stubs if you want to transfer more than their monthly limit. I'm not sure exactly how much that presently is. I was asked to provide the information with my first transfer of $1200 USD. There's no problem with $500 a month. Keep in mind you will only receive Argentine pesos, not dollars.
If you apply for a resident visa your foreign source of monthly income will also need to be documented and bear the seal of the Apostille (any document that has been notarized in the USA can receive the Apostille, including a "cover letter" signed by a bank officer or a CPA).
They will ask for PDF files of your last two bank statements. If you can't comply, your transfer will not be completed. Xoom is 100% safe and the funds will not be withdrawn from your bank account until the transfer is completed and the funds are actually available at the office of their Argentine partner for pick up.
They would also ask for a copy of your passport and the best way to accomplish this is to send them an email with a jpeg of the photo page (which is also good to have in your email vip folder in case you passport is lost or stolen).
If you don't already know, using an ATM card to get cash will result in receiving significantly fewer Argentine pesos than using xoom.com to send money to yourself.
The best rate you will get is exchanging dollars you bring with you at the cuevas in BA.
Use the advance search feature with the key words "xoom" "dolar blu" and dollar blue".
There is also a great deal of info in the archives here about renting an apartment, the difference between short an long term rentals, and paying rent in dollars versus pesos.