Good for you that you are trying to breastfeed while you can, every little bit helps. So, here's what I can tell you. Breastfeeding does not have to be all or nothing. If you wanted, you could probably still nurse your baby girl in the morning, and then in the evenings after you are home. Depending on how often she's eating, you may be able to nurse her 3 or more times for a long time while supplementing with formula while you are at work. I just wanted to mention that b/c it seems most people think it's an all or nothing thing. Ok, I"m not sure about the transition to formula. I think you mix it until it's all formula, but if she takes the formula fine, you may not even need to do that, you could just give breastmilk until you run out and then give the formula, but you should probably check with your dr. on that. As for weaning, I always dropped 1 feeding per week until I had the feedings I wanted. For example, you know you are going to need to drop her 10AM feeding b/c you'll be at work, so maybe drop that one first. Keep the 1st AM feeding b/c you can try to nurse her before you leave for work or you can pump that one if you want since you'll probably have good milk supply at that first one of the day. The next week, drop the next feeding that you need to b/c of your work. You'll have to figure out how many weeks out you need to start based on when you are going back to work and how many feedings you are trying to drop.
If your nipples are sore and cracked, she probably isn't latching on properly at EVERY feeding! It's tough at first to get that down, but if you aren't sure if she's latched on right, take her off and try again, it will save your nipples! You can also try applying Lanolin on your nipples after your feed. Just a little, and you don't have to wipe it off before your next feeding either. Good luck!