Yes, training/targeting abs directly will help strengthen the muscles around your midsection and improve your posture but it’s going to have little to no impact on body fat levels (unless you're burning thousands of calories from your abdominal training.... and you’re not trust me)
Being in a Calorie deficit burns fat, if you're not already in a deficit then taking fat burners will not put you into a deficit big enough to notice any notable fat loss effects. However, they can be very useful fat loss tools especially at a later stage in a diet where results are slowing down and you need an extra push.
Fat burners will increase your heart rate which will increase calorie consumption, they will increase your energy which, when in the later stages of dieting will be very welcomed and they suppress your appetite which can make your calorie restrictions much more bearable.
Overeating and consuming more calories than you use will make you fat. If you eat 200g of Carbs a day but are in a 600-calorie deficit you will lose bodyfat, if you eat 75g of Carbs a day but your Fat/Protein intake puts you in a 1000 calorie surplus you are going to add bodyfat. Some people are more sensitive to certain Carbs than others but bloating and water retention is not bodyfat.
One of the biggest myths out there. If you consume 2 meals at 1500 calories, or 3 meals at 1000 calories or 6 meals at 500 calories if the total is the same there will be no difference in weight/fat loss. However other things may suffer. It isn't ideal for your digestive system to eat 2 x 1500 calorie meals as your daily intake, you are likely to bloat and probably feel sick. The reason why most opt for smaller more frequent meals is to give your body opportunities to have quality nutrition at more useful points such as breakfast/pre-workout/post workout/pre-bed, as well as making you feel like you're not as restricted with the amount of food you're eating, especially when dieting.
Your body doesn't know what time it is, if you're training well and are active you need to constantly fuel/recover. Just because you are asleep doesn't mean you stop using calories, quite the opposite. Many studies have shown that the food you eat up to 24-36hrs previous can have a vast impact on that time in the future. So, if you're training legs (or any session that is going to be particularly taxing or require a lot of effort) on Tuesday you may want to consider upping your food intake from Monday afternoon. Try it and see :)