Benfica to Old Trafford?

The lad is the top assister in the Champions League I believe and whilst playing outwide at the moment for Benfica he's supposed to naturally be a CM. On paper he's another player who fits the bill for what we're missing in the central midfield, he's direct, creative, knows where the net is and can split the defence and play the killer pass. A few things worry me though, firstly the step-up from Portugal to England, something we've been quite successful with before but they've always taken a couple of years to adjust and already at 23 can we afford to wait? Secondly, he's Argentinian and we all know how that tends to work out for us. Thirdly, he struggles to get into his national team so will that mean work permit issues? Also teh fee involved, 25 mil is too much for a player unproven at Premier League level, if it eventually rose to 25 or even 30 mil depending on performance then gair enough but as an outright fee we could spend better elsewhere. His stature as well, he's what 5ft8? The best players have no issue adapting to the premier league whilst other small stature players don't tend to make it.