My impression of Ivan the Terrible is that he wasn't so much crazy as utterly ruthless.
IIRC the Muscovite Princes were just uniting the Russian principalities into one state at this time, so I'd guess that the major question facing Ivan V would be which direction to go in. East is full of nomads, steppe tribes and other annoyances of both pagan and muslim origin and varying degrees of civilisation. West is Lithuania and in fairly short order Poland-Lithuania, which is a bit of a tough ask - although there were quite a few Russians and similar within the nebulous borders of the Grand Duchy. South is the remnants of the Golden Horde and the Crimeans Khanate, which is supported by the Ottomans. North is Sweden.
I'd expect some aggression towards at least one of these, and quite possibly some thoroughly vicious internal politics. The major questions of the reign will be who does he marry and does he have a son.