First, let me apologize for the delay in answering your questions. I actually took a vacation. My answers will be suggestions only (for the time being). BANA is in the process of finalizing a set of guidelines for graphing calculators.
Y1 = sin x Yes, capital y followed by dot 5 number 1 as in print. Boldface should be indicated in braille. As for the two different ways of expressing y sub 1, follow print.
In the keystroke Y=, do not insert a space between the Y and the equal sign.
In keystroke X,T,(theta),n insert a space following each comma.