My thoughts (from a fellow tinker):
for #2: If your carbs go over about 100g you will throw yourself out of ketosis. How long does it take you to get back into ketosis? For me it's around 5 days. Some people say they do after a day. For me, it would not be worth it as by the time I get back to burning fat, I'd be eating fruit again tossing me back out yet again.
For #1 and #3: The only thing I can say is the meals are formulated to give you 20% of all your vitamins for the day. This is why they say no daily vitamin (otherwise you can seriously overdose yourself) while on the plan. If you drop a meal you are not getting your full vitamins. Not that I'm saying don't do it, it's just the only thing I can think of that might affect your decision.
#3 sidenote: I order the diabetic shakes as they have less carbs. Medifast has stated that anyone can drink it as it's not formulated solely for diabetics.
Have you looked into the 4-2+snack that is listed in the diabetic materials? Some people report to have better luck with that plan then the 5-1 plan. Also I recommend browsing the "Dietitians Support" forum on the mymedifast site.
I do not believe that sugar = craving. At least not a ketosis levels. If my carbs are 90, the average 70, or the rare 50, my cravings are the same on medifast... zero. Now if I'm off medifast and I'm eating 200+ BAD sugar carbs (refined, soda, junk food) I will have cravings.