Manafort was a yuge part of Trump's campaign team , so why shouldn't he be questioned to the fullest ?
I have never been a fan of the "blank check" special counsels. Wasn't in the 90's, am not now. The Judge is perfectly within reason to demand the prosecution provide Mueller's "scope memo". It has a direct bearing on Manafort's case.
The judge seems concerned that there is a line between crimes discovered incidentally, as you reference, and just using the office as an excuse to conduct an intense legal audit of the person's entire life. The Special Counsel is granted extraordinary powers and independence, but it exists on shaky Constitutional ground. So it is not without limits. Exceeding those limits is the road to repression. It's not like the whole Mueller/Comey/McCabe/Rosenstein cabal has ever evinced much concern for fairness or civil liberties. Traditional liberals would have instantly seen that. The Justice Department is part of the Executive Branch and thus subject to the President's direction, not that of congress or "career professionals" (ie democrats) employed there. If the congress objects, they are not without weapons to use to fight back.
I am not in favor of special counsels especially when no crime has been committed. Special counsels, including Kenneth Starr go off on tangents that have nothing to do with the initial directive and seek to find something/anything? -in order to appear that their appointment was justified. --The sad part is that the special counsel serves at the pleasure of the president, yet politically he can't be fired. Thus this makes the SC the most powerful person in the country usurping the authority that the voters have cast to the president. ---Kind of the way a fed district judge thinks they can stop anything a president does just because it doesn't fit their own personal beliefs.