Congratulations on the success of your fast thus far! I hope you achieve all that you hoped to accomplish!
I'm not sure about where the gas comes from... but I do believe it's a normal part of the elimination process. There have been a number of posts here where people mention having gas. (and cautioning against expelling it anywhere other than the toilet, lest you get more than you bargained for!) :)
Isn't it funny how one starts fantasizing about vegetables while on the fast? I started mine craving pop tarts and ended craving salads! Hooray!
As far as eating favorites in moderation goes... I haven't actually had "splurge days". I have allowed myself to occasionally eat things I like in moderation, i.e., on the cruise I was just on, I would eat fruit and salads all day, have a vegetarian dinner, then allow myself one dessert - cake or frozen yogurt - after dinner.
Many of my former favorites are no longer favorites because my body doesn't react well to them.
In the five or so weeks since I ended my 22 day fast, I've looked at my eating as sort of a Science project. It's been interesting to see how my body reacts to what I'm eating, and easier to pinpoint what foods are causing what reaction. I weigh myself every morning as a part of the monitoring process. Aside from feeling foggy or gross when eating certain things, it's amazing to see how the scale can jump after eating certain foods, then dial back when I don't eat them for a day or two. Therefore, it seems that my body "corrects" itself when I listen to it and adjust my intake accordingly.
The only negative affect I feel I have experienced is that the first time I ate pasta after my fast, I began craving bread and bread like products again. That was one of my food addictions (that and chocolate), and it was gone after the Master-Cleanse until then.
I suppose the bottom line to what I'm saying is listen and respond to what your body tells you.
As far as the frequency of MCs.. I've heard different things, like that some folks do it four times a year with the change of season; some feel twice a year is plenty; others feel you can do it whenever you feel your body is telling you to; there's a girl where I work who does it 10 days out of every month. I don't remember what, if anything, Burroughs' text says about frequency.
All the best to you on the remainder of your fast, as well as the journey you begin at the break!