Mind if I Stay a Few Days?

This is the wrong way to phrase this request.  The proper question is, "I would love to see you, are there any days in August that are convenient for you?" Never ask for more than 3 nights. EVER! The only exception to this rule is when the person has a whole guest house.  

They might be able to tolerate one or two extra days.  But we wouldn't suggest pushing it.  Your host becomes a prisoner in his own bedroom, and the guest is unaware.  Your guest wonders why you stay in your bedroom all the time, and the host wonders why you never vacate his favorite chair.  Always, always, always leave people wanting more of you.  The stench of you overstaying is impossible to scrub clean and will taint a friendship.  And don't forget, if you haven't been able to pick up copious dinner checks, you cannot go overboard with the thank you gift.