Use the VVP to purchase 20 apps anyway, you may use the licenses later when you get additional iPads. For example, Book Creator for iPad is 4.99 (1-19) or 2.49 (VPP minimum of 20), 2.49 * 20 is 49.80, cheaper than buying 10 at 4.99 which is 49.90. Buy 10 get 10 free. If you will ever need 10 or more of an app VPP is the way to go. (Unless the app developer doesn't give a discount, some don't)
Doen't help with ordering, but is a nice guide.
Excellent guide. See announcment post -- https://discussions.apple.com/thread/4256735?tstart=0
good tips for initial deployment: