6pm through 8pm is rush hour for leaving the city (your direction). I had no problem this week as it’s still early January (summer holidays) but during the year it is usually quite bad. I would estimate 1.5 hours just to be safe.

Fast Pass is not necessarily for Business Class – I travel AF and security staff won’t let me use it despite my boarding pass showing Sky Priority. I think other airlines may have it, but I’m not sure. Otherwise I know you can buy it for 20 USD from the EZE website.

As others mentioned, both transfers seem very tight. I would also book a flight out of USH in the morning just to play it safe.