I've purchased 21 so far and 4 are on the way from NFC.
Normally, my main goal is 36 (one platoon,) but since I've already gotten the Sergeants in the form of the Tantive IV stomies, I only need 32 to make the platoon. However, I decided that this trooper, with the helmet off, makes a great Lieutenant, so I've taken 4 and added rank insignias. ( 1 for each of my 4 Platoons.) I'll need to replace them, so in the end I'm picking up 36 anyway.