“I also guess that a minimum of 20-30,000 do not understand a Yiddish speech.”
This is way far fetched. At most 15% don’t comprehend any Yiddish.
“1. The number of Yiddish speakers in America drops significantly every year. 7.5 years later means a big drop.”
This is the opposite of reality. Chasidim with their much higher birth rate are an increasing majority of American Orthodox Jews. And hence the Yiddish speaking proportion of American Orthodox Jews is increasingly rising.