I'm having a concrete patio poured that is 760 sq. ft. I need to confirm what the depth should be. I thought I read 6" but my contractor is telling me all I need is 4" for a patio. It's not like we'll have a car parked on it. It will have an outdoor kitchen and firepit though. Can someone confirm the correct depth? Thanks.

4" is more than adequate for a patio. If you are planning on having a open fire at ground level then this area should be left open with a ring poured.

What should the concrete depth be for a pathway that's roughly 2'x100'?

Patios and sidewalks are usually 3 1/2" thick. That's why I said MORE than adequate. http://www.quikrete.com/ContactUs/FAQs.asp