I don't think the wolff book tells us much new in and of itself - what it does do is firm up the idea that Trump is a capricious, infantile, bullying dimwit with questionable mental health surrounded by chaos. Indeed Trump's response to the book has only reinforced that perception.
What i am wondering is how long will it be before Trump loses his shit to the extent that he is clearly incapable. I have a lot of issues with the shrink assessment of his fitness for office - but the notion that the stress of the FBI investigation will lead to ever more erratic and destructive behaviour does ring true (the whole "biggest button" thing is gobsmacking really - its like some OTT, dr strangelove-esque satire but for real). The wolff book may become a self fulfilling prophecy - in that it provides the final nudge that pushes Trump over the edge. Or maybe a pummelling in the mid terms will do that.
How much cover could Trumps circle provide if trump does become truly incapable? they are not the most discreet and loyal bunch are they?