Possible 40 day water fast for a slimmer stature? Tips and advice would be very much appreciated...

The longest Water Fast I've managed is 9 days. Tomorrow I begin my journey on, initially, a 7 day water fast. And depending on the way I feel then, I'll carry on to, ideally, complete a 40 day fast. However, my weight is a bit worrisome. I have quite a few health woes I'm hoping to combat with this fast, candida overgrowth in my gut, acidic body in general, stubborn angular cheilitis, and a few other issues, including nerve damage. I'm a refined sugar-free vegan, and I stick to moderate/low-moderate carb intake, so I believe my diet will be advantageous in this journey as the transition won't be from addictive, processed foods to nothing.

But, like I said, my weight is one thing that might get in the way. I'm 5'9, 23 and weigh approximately 130 lbs. Typically, this wouldn't worry me too much, but I have very little fat on me as I'm more lean muscle than anything. Would it be wise, at my current weight, to endure such a lengthy fast or should I look to a more sensible one of around 21 days?
Also any advice would be very much appreciated. Particularly, would electrolyte supplementation be necessary on such a lengthy fast?