I do daily 18/6 IF (eating between 2:00-8:00pm). Roughly once a month, I'll realize I'm not hungry and fast straight through until hunger returns (usually 40-60hrs).
I tried alternate-day fasting. I also tried doing one complete fast day per week, on top of my regular IF. And both were just too much--instead of feeling good, I felt anxious, and felt like I was setting myself up for a binge. So back to regular 18/6 I went, and everything's cool again.
Fasting has tremendous health benefits, and it's a useful tool, but it's also a stressor. So if you're having physiological or emotional stress reactions, go easier on the fasting.
As far as exercise goes, there's nothing I can't do in my day-to-day fasted state. I'm in ketosis, my blood sugar's stable, and I don't get weak or dizzy. On longer fasts, I take it easier--walking, but not running or doing anything particularly strenuous. I figure if my body's asked for a break, I'll give it one; it's not going to set me back if I postpone heavy work or intense activity for a day or two.
I'm not even sure what my caloric intake is, now. I eat whatever good food I'm hungry for, in the quantity it takes to satisfy me. Some days, it's a lot; other days, it seems like hardly anything. If I'm consistently not getting enough to eat, I'll get ravenous and eat stuff I probably shouldn't, so if I'm hungry, I eat, and don't get hung up on whether it's too much, or how many calories are in it. I've found it's pretty hard to overeat when I follow hunger/satiety signals and eat nourishing food. But it's hard deprogramming from decades of worrying over calories and portions and good food and bad and loads of shitty diet advice--WHEW. To just eat what I am truly hungry for, to satisfaction, has been kind of a leap of faith. It does seem to be working really well, however.
Oh, and hair loss--yeah, I got really sheddy for a while after going VLC, and the first three periods after starting were just insane (instead of Shark Week, it was goddamned Shark Fortnight).. But I felt so good otherwise I decided to ride it out for a while, suspecting that things would eventually go back to normal. And they have. No more crazy periods, hair's growing back in like mad, and I feel great. VLC is definitely not for everyone, and the transition can be rough, but for me it's my happy place.