I tend to be conservative when it comes to my horses and I certainly overly cautious with conditioning, but I want him to continue enjoying driving, so I don't want to overface him. There's a great conditioning schedule on (as well as a lot of other great info) on minihorsecde.com
We have a great driving resource with Happs in Ethel, WA. Maureen Harckom is a great advocate of minis (or VSEs, as they are classified by ADS) and has numerous driving events throughout the year, including their big CDE next weekend (June 18-20). There are some excellent teachers up this way and many knowledgeable mini drivers (I'm a newbie comapred to them). We also have a group called NW Beachdrivers, a very loose organization of folks who get together each fall in Long Beach to camp and drive (or ride) our horses on the beach.