"I have the Guide to the JMT by Kathy Morey with the Tom Harrison Topo maps included within it. Is it a necessity to have the actual Topo Maps by Tom Harrison? I plan on taking the Guide Book with me on the hike."
I'm hiking the JMT starting in a couple of weeks, own the guidebook, and personally I'm bringing the real Harrison maps and not bringing the guidebook. I've copied relevant info from the guidebook onto the backs of the maps. The JMT is a big, wide, well-maintained, heavily traveled trail -- BUT I would still feel very vulnerable hiking it with only those tiny, simplified, black and white maps in the Morey book. You can't see the green markings for forest. There is no UTM grid (are you bringing a GPS?). In a lot of places, I would have trouble making out the microscopic elevation labels on the contour lines. I would consider even the real Harrison maps to be a little on the condensed side, compared to a 1:24000 usgs.
"Are there any particular stretches on this segment of the trail which are void of water for some duration? How much water should we carry at a time? I was thinking 32-34 ounces."
You can go through the maps and look at how far apart the streams are. I haven't hiked that section yet, but it looks like there is plenty of water. How much water to carry is a matter of preference and opinion. Here is some information on the wildly inflated urban folktales about how much water you need to drink: http://www.lightandmatter.com/article/hiking_water.html IMO a perfectly valid answer is to carry zero water on the trail; just drink when you get to water. For various practical reasons, however, (e.g., you might not be camping near water), you probably want to bring at least some water containers. I'm bringing two half-liter water bottles of the type they sell bottled water in. Your choice may also be influenced by what water purification system (if any) you decide to use.