First of all, you should be Argentine citizen for joining AR as a cockpit crew.
There aren't bases, everybody reports at Jorge Newbery Airpark or Ezeiza Ministro Pistarini Int'l airport.
For this year and for the next, I do not see any hiring unless you are part of the Campora party. AR has around 1300 pilots at this moment and it is known that they have more than they need for its operations.
Upgrades can range between 6 to 18 years depends on the situation of the company.
I don't see a bright future for AR if the government party change in next year.