As for a stop loss, again, depends on your risk appetite. Many will place just below the lower of the orange lines for the flag, so extending the line over to tomorrow (29 May), it would be around $89.50, or just below $89.30 which is a defined support/resistance line.
Anyway, different people play it in different ways. So work out what works for you and you'll be sailing. Having said that, I'm very overweight on BABA on my portfolio, so I do not yet know if am going to play this one.