Hi PinkPurple,
Like you, I have never stratified zinnia seeds because, as far as I know, zinnias don't depend on cold treatment to make their seeds viable.
Regarding your State Fair seeds experience, State Fair is a tetraploid zinnia, and their seeds are expected to behave differently, depending on whether they were pollinated with non-State Fairs. Your friend's Profusions may not have been well pollinated. Belize is an inter-species cross similar to Profusion but grows only about a foot tall.
Regarding your fourth question, there is little correlation between seedling height and ultimate plant height.
ZM
