If your blood type is A, you will mostly benefit from juice fasting. You will need a good kitchen juicer.
You can juice carrots and many kinds of vegetables. Also fruits low on sugars, like some berries, lemon, etc.
Also smoothies can be OK.
But, keep it low carb.
Other blood types can try either one of those, Keto diet fasting or low carb juice fasting.
These fasts (diets) can help lose weight, and you can do it or many days, weeks, months.
If you combine it with walking, light exercises, weight lifting, you will lose weight even faster.
Foods that make most people gain weight are sugar, grains, milk products, sugary fruits juices, and industrially processed foods.
Some people can gain weight on a 100% fruit diet, if you consume a lot of fruit juices.
So, generally, keep it low carb, it will give you fastest weight loss.
What about water fasting?
Water fasting is one of the fastest ways to lose weight, but unless you continue with low carb or keto or juice fasting after, you will get all your weight back, and even more. Hunger makes your body much more efficient in absorbing food and storing food for later in the form om body fat.
So, if you just want to lose 20 kg in 20 days, start water fasting.
If you want to change your life, be prepared to go on a specific diet after the water fast, so you do not get 25 kg back in the following 20 days.
"How long does an initial fast run?"
If the question is about water fasting, you can plan it for 7-10 days.
The first 3 -4 days are the most difficult, so once you are over it, you can fast as long as you feel OK.
"when does ketosis typically kick in, and how do I know that it has?"
There is urine test that can show if you are in ketosis, but that is not important.
It will kick in during the first 3-5 days.
You do not have to know if you are in ketosis or not.
Once your hunger is 100% gone, that is the best sign that you are in ketosis.
"how much water/juice should be taken, each day?"
On a water fast: You drink per thirst. Clean water, as clean as possible. Filtered tap water is better that unfiltered.
Good bottled water may be good, especially if it is sold in glass or hard plastic container.
On a veg juice fast: you drink per thirst and per hunger.
Juices are both food and drinks. The best is to drink fresh juices, but it is Ok to make juices in the morning, and drink it during the day. You bring several bottles of fresh juices with you wherever you go.
"how is either fast broken?"
water fast is usually broken with some fruit juices or soft fruits like melons, over the course of several days.
The longer the fast, the longer the breaking time.
After 10 days water fasting, plan on 5 days on juices.
After 20 days water fasting, plan on 10 days on juices.
You can also do several days juicing before you start water fasting.
Or several days on keto diet before the water fast.