You can reuse the nut, but a new nut comes with the new shock.
Any normal jack will work to get the shock out. Jack up in the normal spot, just use a strong piece of wood with larger jacks (3 ton) to avoid destroying the jack point and it will be fine. A smaller jack will fit in the spot fine.
Having 2 people helps as sometimes you need to stand on top of, or jack up the control arm to line up and get the new shock back in. There's not much space in back, and be sure to note the orientation of the shock/spring as it has to go back in the same way. The best way is to mark one of the 4 bolts on top.
I'd say 2-3 hours based on experience and available tools to do just the rears.
4 wheel alignment will be around $100 pretty standard.
Did you replace the front shocks already? If not, do them all at the same time.