Hi- The day before this wonderful post went up, I had reread the Pachypodium special issue from the CSSA Journal, July-August 1996, Vol. 68 #4. There's a wealth of excellent cultivation info in there, sometimes a rarity for the CSSA journal.
The healthiest and most compactly grown, robust Pachypodiums I ever bought were from Highland Succulents. Arid Lands has great plants as well but they seemed a bit more leggy, sprawling and less shaped than the Highland Succulent ones. At Highland, the prices can be higher, but I like the shipping and the quality.