On the flywheel nut you can www SAE fastener torque specs, find your size and go from there. On my 90 it was over 100 ft-lbs. So as a guess a 90 vs 4 is about 20:1 so about 5-10 ft lbs. You probably have a Woodruff key in the flywheel and the two should hold unless you hit something with your prop at WOT which possibly could force it to slip out of position. A distorted Woodruff key and hard starting would attest to that.
On the prop, same thing or when grasping the prop in one hand and wrench in the other, good and tight, which is defined as uncomfortable trying to hold one prop blade with one hand.
