I had really low energy when I did my last fast for the first while. I started on water and then went on juice and noticed a definite energy boost after even an ounce of juice. Personally I think if you have to have energy I would take some juice.
You can expect to lose about a pound a day. Generally people lose more at the start of a fast (good thing too because it is the hardest time).
Hope others will post more to help you out...I'm still a newbie faster. :)