Yeah I would. "Best" doesn't mean expired to me. It's probably not as strong in nutrients as a fresher one but I wouldnt be worried about it causing problems.
Yes, I would. In fact I may have given DS expired Pedialyte earlier this week - it's been in our fridge for quite possible a year. My mom works for a company that does grocery store logistics so she brings us expired food all the time! We are still alive, and she's worked there for 5 or 6 years now.
Nope, but Ive always been strict with expiration dates.
Somewhat related freaky story. I had an old Co worker that once took expired tylenol and he went temporarily blind. I can't remember all the details now but that has always stayed with me. Now when I see an expiration date I think, nope, dont want to go blind.