Re: Best way to use formula
Before you pump and dump, contact the Infant Risk center http://www.infantrisk.com/, (806)-352-2519. Moms are often given overcautious advice concerning medications and breastfeeding, and it is possible that you don't need to pump/dump at all or that you don't need to do so for the full 18 hours.
If you need to use formula, ideally you will offer breastmilk and formula in seperate bottles, since the storage guidelines for breastmilk and formula are very different; unused formula must be discarded while unused breastmilk can be reused. I don't know if there's any additional advice I can give that's guaranteed to be useful- it all sort of depends on whether or not your baby will take a bottle of formula!
Good luck tomorrow!