Aw, SJ I am so sorry you are sick! That is so not cool right now
If you like, you could try a different hold for the nipple that is cracked. The football-hold may not open up the crack as much. As long as it's not too painful, I'd say just keep on with it. It will heal up - give it some air and some sunlight (not too much sun - don't get burnt!) and that will keep it dry between feeds and give it the chance to heal. If it stays too wet (like any wound) it isn't likely to get better as quickly, KWIM?
2-3 hours sounds great to me.
IRT how you know when to stop feeding, this was a big deal for me too. The fact is, it is up to you. No one can tell you when she's done, you just make the call. If you want to feed her round the clock, go for it. If you want to stop after 20 minutes, then stop and settle her a different way. It's up to you, and neither way is wrong.
Good on you, SJ. You're amazing