A) you’re right that you need to get enough nutrition to see you through your fasting period (rather than just calories). You need to get enough sodium, potassium, vitamin B, etc during your meal so that you don’t get a deficiency. Otherwise over a few prolonged fasts you may start to show some uncomfortable symptoms.
B) you should lose weight at a healthy rate - (I believe) losing too much in one go can be stressful on your heart/organs. So you need to calculate your maintenance calories (eg 1700), then figure out your appropriate calorie deficit to lose weight (eg 500), and then make sure you eat the proper amount of calories to strike the balance (~1200). There are calorie calculators online to find healthy amounts for your height/weight etc. It’s not like ‘more is better’ or just because, it’s about striking the balance.
C) if you continuously eat too few calories you will enter starvation mode and your metabolic rate will slow, your weight loss progress will struggle. You need to occassionally tell your body that you’re not starving, you’re getting the energy & nutrients you need, but between meals you’re relying on those fat reserves.