Hi Nichole! Ditto what everyone has said... you'll do fine and will probably be really surprised at how much fun it is. We gave a tour, but it was a stand-in-the-doorway kind of tour where she just sort of peered into each room. I really think they should rename "homestudy" to "family study," since that's more of what it is... although there are a LOT of super-clean homes as a result!
As far as food is concerned, do whatever you feel comfortable doing so that you can relax during the interview and not be riddled with questions of "should I have/not have offered something?" I'm a big believer in just going with your gut.
Our SW also came around dinner time--I think it was 5, 5:30 PM. We offered coffee, she just asked for water. I suspect that when they have appointments at this time, they might grab a quick bite on the way to your house.
By any chance is Henrietta your SW?
Best of luck!
Christina