He's already better at linking play with his back to goal than Chicharito was. Tidy with short flicks to anyone running near him.
I don't think he'll be a right winger. Players like him don't really play there anymore.
I can't really think of a really effective attacker in Europe who is at their best on the same wing as their strong foot. It seems to be obsolete. Nobody at Barca, Bayern or Real does it. Bellarabi plays on the right normally, but maybe he'd be even better on the left cutting in. And he's more good than great. Atletico use Koke on the right but he'd basically just a playmaker standing out wide like Milan or Madrid Beckham (young, faster Beckham was more a normal winger).
If Rashford keeps looking this good, I think it'll be Martial, Memphis and Rashford as the 3 players we need covering the 9 and LW positions and we will still need to sign a left-footed to play on the right like Bale, Griezmann or Mahrez. And Januzaj (also a 10 option) and Lingard will be fighting to win the spot as that player's backup.