To be honest every point you say I would argue against.
If we need a replacement for Rodri and Pep wont trust players with significant of european and premiership experience I would be surprised if he would use a player with no experience outside Brazil immediately, therefore resulting in Rodri not getting any rest at all this season.
We have just done a couple of transfers in midfield at fees which could be argued are at low risk, with the end result being players sat on the bench Pep wont trust. Its a false economy for me, buying because the price is right, but then seeing those players just sit on the bench and not make a meaningful contribution.
If the lad is good enough buy him to replace Rodri if not go out and aim to but someone who can.