A lot of people make the lemonade drink ahead of time:
48 oz water
12 tablespoons syrup
12 tablespoons lemon
3/5 teaspoon cayenne (or to taste)
In The Master Cleanse book, Burroughs states that no medications or vitamins be taken while on the cleanse, as they can trigger your digestion and interfere with the cleansing process. Since you're not eating, you shouldn't have a problem with heartburn, and if you do, you might want to attempt soldiering through as it could be part of the detox process, but in the end, we all gotta do what we gotta do. :)
In regard to the SWF, it was my understanding from Burroughs' book that it should be at least lukewarm so that it mimics your body temperature, and relaxes your colon. Otherwise, the salt could be absorbed by your body. It should also be ingested all at once, as quickly as possible to create the "flush" effect.
It is also my understanding either from the book or from years of posts here (not sure which) that the lemonade drink should be taken room temperature or cold, but never heated, as heat kills the enzymes and nutrients from the lemons. For the same reason, the drink should also not be made the night before and allowed to sit overnight before drinking.
And yes, you can take Epsom Salt baths while cleansing. Many people feel it helps the cleansing/detox process along. Body brushing or loofahing in the bath or shower also helps.