First, I want to start off by saying that "food combining" has not been shown by science to be something that everyone must stick to. This approach is often used by those who have digestive issues. Protein combined with carbs is actually necessary at certain times - like for example after someone exercises to replenish lost glycogen stores and to help rebuild and repair muscle tissue.
So, that being said...don't fret about the combining unless you have digestive issues. I would avoid dairy while on the transformation plan. I've had several people feel better and lose weight once they give up the cheeses and other dairy foods.
To answer your questions...When you say cereal, I'd say steer away from the cold processed cereals. These are often laden with sugar and are mainly refined carbs. If you'd like cereal, a nice bowl of gluten-free oatmeal or quinoa make a great breakfast!
Popcorn is considered a whole grain - just be sure to get organic, non-GMO corn as most of our corn is genetically modified. It is a carb, but it is a whole grain with a reasonable glycemic index and low glycemic load which means it won't spike blood sugar as much as a processed, refined grain do. It is also low in calories and high in fiber so if you are trying to lose weight , then it is a great snack option. Just be sure you don't overdo it - too much of anything is not good.
Food is about 70% of the weight loss equation, with exercise as 30%. You need both for optimal health! Try to fit in anything possible - even just a light walk for about 15-20 minutes and then work up from there :) You will most likely see changes if you just stick with the NutriBullet plan, but adding some physical activity will kick it up a notch and provide additional benefits!