don't forget that one of the first steps is driveshaft removal, that can go smooth or take a weekend in itself. if all goes smoothly i think 2 weekends is probably a good estimate if you already know how to fiberglass. start by taking the shaft seal off. might see if the shaft wants to go easy or hard too.
as to what caused it, the prop strike might have. i suppose a handle could too. i could see it getting wedged between shaft and hull and causing some flexing.
the closeup looks pretty nasty. that's a really bad spot for a flimsy patch on a big problem...if it is big. still hard to say from here if a temp patch is possible. you're gonna need to open her up a bit before you can plan an attack. a crack is easy to fill but a crunched area is a bigger deal.
okie's on the road otherwise i'm sure he'd have seen this thread.