As we all know, tutorial missions aren't really that lengthy so Barret would most likely be getting like just a few screen/game time to get players to know him, but since this is a fan game and also the final (or so I've heard) game in the series, we could go prolong it a bit by introducing contents(skills, movements, default weapons, vehicles etc.) not familiar to fans of the series. Of course his screen time heavily depends on what the devs plan to add to the game that wasn't seen/heard of from the 1st 2 series.
Though I have never heard what Barret's role is in the game, could I propose him to be the Junk shop dealer? Judging from appearance, Barret seems suitable for the role imo.