After having a conversation with fellow builder Wayne Orr, I shimmed up the omni-wheel so that the foot sits level with the drive wheel. As you can see from the photo below, the level shows that its all nice and, well, level!
Wayne Orr, Victor Franco and Mike Senna have been enormously helpful with the questions I have had regarding the center foot. I had three 2" omni-wheels mounted in there. However, from what I have heard from others, the best way to go is with a castering wheel, ideally one made of a very soft material. I am in hopes I can find two 3" ones that will be able to simply bolt into the mounting plate I have already. Here's a picture of how the center foot looks now, while I research the castering wheels more.
And yesterday the UPS man brought me goodies! This is the aluminum skirt and I intend to use this on droid #2. Darren Murer was kind enough to sell me his. I missed the original run and these are not made very often!