I can’t comment on the amount of time you wanna fast. But know that if your goal is to lose weight, some form of exercise will help a lot. Just don’t do heavy exercises when you fast! I personally just like to walk a lot :)
And weight loss and staying on weight is as much as is it about the mindset as anything else. For me it always helps to remind myself I do this because I wanna feel healthy, because I deserve to be comfortable in my own body. When my motivation comes from a negative place it’s much harder. So find the right motivation, from a place of self love instead of self hate or self depreciation