Re: question tag
As riquecohen says, you need to use context to figure it out.
You would rather = common
You had rather = not grammatical in current use.
However, I'd tag it with "wouldn't you" instead of "would you."
The statement is "You would [rather not]," so a negative tag is more natural. It's not "You [would not] rather. At least, that's how it works to my ears.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.