Uhhhh...if you are dead set on doing exercise along with being on your feet so often at work, I would say that a water-only fast would not be practical for you. While I personally choose to water-fast only, I also make sure that my exercise levels and work-on-feet time is drastically lower than usual.

It sounds like a juice fast with mixed in days of water only (most likely your days off from work) will be your best option.

Eight hour shifts of making food all day will not be very kind to a water fast. I would recommend mostly juice for the good majority of the fast...don't even bother with a water day until you are starting to feel re-energized from the juice...that way you know you can actually make it through the day.
Keep water days to days off that way you can relax...
and three hours of walking seems like a lot. do you already walk that much? If not, I would stick to 30-60 min of walking. You don't want to shock your body too much.

When I first started fasting, I lost a substantial amount of weight. I didn't exercise much while fasting, but when I was on solid foods, I did exercise a lot. I don't know how much I lost on fasting alone, I didn't really weigh myself often and that was probably the key to my success- if the scale doesn't show what you want, you may get discouraged. I didn't even realized I had lost 70 lbs until 6 months later when my college roommate, sister, and I all compared weights. I was in shock, actually, to be 104 when the last I checked I was 175.