Being fairly ignorant of the topic, although presently losing weight myself, I suggest stop doing the exercises most fat people do- wel, not stopping, but altering them. Instead of the alternating doughnut curls, try substituting glasses of water. They are a little heavier than the doughnuts and have the added resistance of the glass when returning to the starting position. If you have built yourself up to maybe six doughnuts a set, two or three times a day,try beginning your set with one doughnut, then finish the reps with the glasses of water. This works equally well withh Pizza lifts and candy curls also. During meals, Eat one plate of food. Stack it rediculously high if you want, but no more than one plate. Find a sensible desert, and have that. When you walk, have a goal.every week, increase the distance to half of what you think you can do, an extra quarter mile instead of an extra half mile more. And really, as extra motivation, as far as motivation goes, chicks dig men they can put their arms around.
As far as martial arts goes, I know less than about weight loss. So here is my opinion on that. You are already practicing the basic premise of walking away from a fight, Excellent! AS I am losing weight, I have noticed my strength is decreasing, but my endurance is increasing. My flexibility is poor. If I were leaning towards a martial art, I would select a school, and ask them which exercises for flexibility they would suggest and then set a goal as to what weight I would hit before actually starting lessons. Two reasons- not taking on to much at one time, and rewards for the smaller efforts made. I found that charging full bore into diet, exercise and added activites ends in overload. ultimately into failure.
You will do well, enjoy it while it happens.