The Fasting Method has info on various schedules, what you are describing is ADF, which can be done for 36 or 42 hours. Many do it on a rolling basis. It is particularly effective for weight loss and makes use of 2 overngiht/sleeping periods.
If you do strength training the rest of the week (non fasting days) you should be able to keep the muscle. I used to and recently restarted 36 hour fasts, once a week and I definitely became stronger in the process (mass building was never my goal so idk about bulking up and fasting at the same time)
Yes. When you eat excess food, it’s stored as body fat to use in times of caloric deficit. Your body doesn’t eat up your muscles for food. Building muscle is just a function of use - exercise and you build muscle. Eat and you gain body fat. Fast and you lose body fat.