I'd start with a lighter weight that is challenging but not too heavy. You might have to buy another heavier weight as you improve, but i have found as the workout goes on, fatigue prevents me from using heavier weights.
First, don't think of exercise only as going to the gym, although that certainly qualifies. Start, with improving your activity level. For me, I had to commit to not sitting on couch after dinner. Do the dishes, go for a walk, do laundry, whatever. If you want to exercise, that's good too. The best way to get motivated that I found was to step on a scale, look at yourself in the mirror, or try on a pair of pants that used to fit. Then commit to make small changes every day. Good luck, we've all been there.
I incorporate these videos into my routine as well. I find it to be quite effective, moderate difficulty, and actually kind of fun.
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Be patient. I know that answer stinks, but it's true. In my experience in the first couple weeks as you begin exercising and eating better, the weight loss will be slow. After your first month, if you're being consistent, the weight loss will be faster. Of course if you're severely overweight you might drop a lot of weight initially. Just continue what your doing. You mention "nibbling". You might want to be more aware of mindless eating. Eat only prepared meals and snacks.
Ignite allows for lean grass fed beef, so I don't see any reason why venizon wouldn't be okay. It would certainly meet the same definition as lean and grass fed.
I can't seem to get the scale to move either, however I do notice more muscle tone and my clothes fit 100 times better (baggier?) I would use the scale as another tool, not the only tool. More energy, looser clothes, toner face and body? If the answer is yes you're getting results. Also, I suggest only weighing yourself one or twice a week, same day and time. Water gain or loss plays a large role in the final number.
Sounds like you may be overtraining (we don't know your physical level before this). Ignite and Inferno by themselves are quite challenging. You might need to scale back your training, set a list of goals, prioritize them, and then adjust your training accordingly. Also, it's okay to take a day off or modify your workout to do only what you can, resting in between. The DB trainers actually encourage this approach. Just don't beat yourself up and don't quit. You've seen results already so it's clearly working.
I joined the Hydrate All Day challenge.