Rivian Automotive (RIVN 4.31%) reached a big milestone when it reported its first-quarter results, producing a gross profit for the second consecutive quarter. That milestone unlocked an added $1 billion in funding from Volkswagen, which is part of its$5.8 billion overall potential investment. With the electric vehicle (EV) maker starting to get on a roll, let's see if investors should buy the stock before it reaches its next big milestone.Gross profits remain in focus ahead of the R2 launchAfter years of ...