Strictly speaking, any 'flavors' should be avoided during a water fast - they compromise the fast, coz they stimulate systems that should be taking a break. Pay special attn to the correct method for breaking the fast, or you'll create unnecessary grief for yourself. Ketosis usually kicks in around day 3 or 4, depending on glucose/glycogen stores, level of activity, etc.
And no, honey (or similar) defo not recommended during fasting. It will put your muscle tissue in the firing line. Make your last meal prior to commencement of the fast a fatty one to put your metabolism in fat-burning mode.
You don't need to worry about your store of fat to see you thru. The human body has an amazing capacity to adjust to the new conditions without putting vital organs, etc., at risk.
Anyway, good luck when you get there. I'll be starting one myself soon - prob. around 21 days, but might go for longer this time.