I think your three step idea is an excellent start, but your body will know for sure if it's right for you. Do keep in mind that Even After Bowel Cleansing, anything you eat the day before the flush could still be 'hanging around' waiting to soak up toxins and stray 'stones', which is why Clark recommends magnesium sulfate over magnesium citrate as Epsom Salts are a rather strong diarrhetic. As long as you remember to do something to help get the stones out FAST, you should be fine with whatever protocol you choose. (Andreas advises getting a colonic the next day as they really clear you out!)
The Black-Walnut tincture is to kill any released parasites during the cleanse. I include it when I remember, not every time.
What type of medications? Are they the type you can safely skip the evening dose? (Definitely a question to ask a *gasp* doctor if you're not sure.)
I quit drinking soft drinks a couple of years ago and honestly can't drink them anymore - too harsh. That's why I wouldn't do a coke flush as *my* body says "No!" =) One of THE biggies in regaining your health is learning to listen to YOUR body. It's amazing how fully we can tune out our own bodies until the messages become PAIN or ILLNESS.
Lots of people substitute magnesium citrate for sulfate and it works for them.Since you don't get quite the same level of, er, 'clearing' action from it, I'd suggest doing an enema or a saltwater flush the next morning to help ensure the 'stones' are out as quickly as possible. Stones lingering around in the intestines can make you feel very ill.
As to waiting, that's entirely up to your body. If you're ill and just starting to detox, your body may demand you take a break by making you feel tired, fuzzyheaded, joints hurt, any number of detox symptoms. Best to give your body a break during those times, take it easy and just eat well and drink LOTS of water. But, if you feel pretty strong after the initial bowel and kidney cleanses, you can go ahead and do the Liver Flush and then give your body a couple of weeks rest (unless you feel a 'stone' got stuck, in which case a second flush the next day or so is fine, but definitely rest after that.)
For me, the bowel and kidney cleansing were no where near as physically taxing as the liver flush, but other people are almost exactly the opposite. For instance, I can't do a Master Cleanse at all, my body flat out did NOT want to continue after just a few hours (plus, I really don't like lemonade, hehe) but I use the saltwater flush idea from it quite often. Other people seem to thrive on The Master Cleanse lemonade, but can't do the saltwater flush part of it. It really does all come down to listening to what your body tells you.