At present, your core exercise goal is to reduce fat, so muscle training is not your core exercise, so there is no need to eat protein powder at present. As long as the diet is high in protein, low in fat and low in hydration. And protein's excessive intake, on the one hand, will be fatter, on the other hand, the burden on the kidneys is too heavy.
3. The principle of strength training is: it is best to train one part every 48 hours, and you can't repeat training one part every day. The training weight should be 60%~80% of the maximum weight you can lift as the training weight. Usually, there are four groups in an action, each group is 8~ 12. It is required to make the muscles feel tired and not exhausted after completing the reorganization action. When the muscles gradually adapt to the existing weight, the weight should be increased, but the number of repetitions in each group should not exceed 12.
4. The exercise effect of sit-ups is not as good as belly rolling. I suggest you change it to a belly roll.
You'd better do strength training first, and then do aerobic training, so as to reduce fat better.
If you have any questions, just ask.