Baba Rahman has gone from Germany's second division to a €20m move to the Champions of England in the span of a little over 12 months. If that's no impressive enough, thanks in part to Chelsea's early season wobbles, many are already calling for him to get plugged into the starting lineup even. But that's probably a bit hasty.
"It is important because he is a left-back, so he can compete with [Cesar] Azpilicueta. At the same time, Azpilicueta can compete with [Branislav] Ivanovic for the right-back position, so he replaces Filipe Luis in the balance of the squad."
-Jose Mourinho; source: BBC
So it's as you were, except with a backup full back roughly a decade younger than Filipe.
Even if Baba wouldn't need any sort of acclimatization period to our methods, strategies, tactics, and to life in England in general, he probably wouldn't be stepping in straight away for our two entrenched full backs. Perhaps one day, perhaps one day soon even. Filipe Luis was a backup all season long and he still played in approximately half of our games. As one of only three senior full backs on the team, Baba should get plenty of chances. And if he's good, he'll get even more.