My friend told me you could stack his E, more dashes more damage? He also told me that after four dashes his shield instantly recovers. Is this true?
In the past it was possible to stack Yasuo's E up to 4 times. After patch 4.11 and onwards you can stack it up to 2 times. Each time you cast E you generate a small amount of your flow ( More than when you would by walking around ) as well as increase your next E's damage by 25% with max cap at 50%.
It was possible to fully restore your shield after 4 dashes but that is sadly applicable no more, since after a patch the amount of shield he gets restored after each dash got reduced.
Your shield will however get fully generated upon casting your ultimate.