60F rise at 8gpm is about 240KBTU/hr, well over the output of a "whole house" tankless. With a drainwater heat recovery unit as pre-heat for cold water feed to the heater & shower you could probably get there with a standard tankless, but it'd be a squeaker. (~160K from the tankless, ~60K in pre-heat.) Water hardness will also be a mainenance issue, more so with a tankless than a tank.
8gpm for 30 minutes will also be tough. With a 100gallon tank you'd still need drainwater heat recovery to get anywhere near 30 minutes of full flow out of it.