Answer 1 is: YMMV, actually.

Although under no obligation to do so with separate tickets, the AC agent can add Star Alliance partner O6 Avianca Brasil on the bag tags manually which would speed up the connection process after clearing customs. If connection is with LATAM, Gol or Azul then a whole new check-in process would be needed to Terminal 2 or Terminal 1 as other FTers mentioned above.

While I don't love O6, especially if your flight is assigned one of the older aircraft plus no Star Gold lounge access for domestic flights, the checked-thru priority-tagged bags help a bit.