A big part of the answer depends on how often you are willing to test and change the water. At 19 total fish of these sizes in a 29, I think you could be okay. But you should expect to do at least weekly 25% water changes. I formerly, successfully stocked four pepper cory (which I think grow slightly bigger than Sterbai), one ram, four guppies, and seven cardinal tetras in a 20g. But I tested and changed the water religiously. The parameters never got out of whack.
BTW, I'm now rebuilding stock after a "learning experience." I just added four Sterbai Cory myself, juveniles. They don't stop swimming, ever! They are cute as hell, too. And they are happy in Ram-appropriate warm temps that most other corys are not. They cost more, but so far appear to have been worth it.