There's not that much difference between a 4 and a 5. You should be OK with a 4wt. A 5wt will allow you to cast bigger/heavier flies a little easier. When picking a rod, start out with the flies you want to cast. That will tell you what line/rod to choose.

If you're talking to a guy in a shop, I'd definitely pay attention to his advice. He has a better idea of your local situation than I do. This "what's a good starter outfit?" question comes up fairly regularly, and it's usually from someone who's not within 100 miles of a decent fly shop. Arkansas has some good trout waters, so it's not surprising you have a fly shop nearby.

If you buy a rod from him, get him to give you a casting lesson. Or, if they have an "intro to FF class", sign up for it. It will save you a lot of frustration.

BTW, this book I mentioned:

Amazon.com: L.L. Bean Fly-Fishing Handbook, 2nd (L. L. Bean) (9781592282937): Dave Whitlock: Books

... is written by Dave Whitlock. He's originally from Oklahoma, but he spent many years in Arkansas fishing the White River and running his fly fishing school.