If you till the yard you're gonna wind up with more weed seeds than you bargained for. I wouldn't do it just now. Besides, if the dead roots are not in your way, they will provide excellent OM (organic material) for the microbes to work on. Adding top soil to not-so-good soil is always a good idea, but you need to add compost, mulch-mow and leave the clippings (puts close to 40% nitrogen back in to the soil) to increase your soil content. Once the soil is right, everything else is going to grow well also.

And for the record, most folks with fescue yards in direct sun didn't fair well, including me. That's why you need some shade (trees, shrubs, etc) to provide partial to dappled shade to cool those grass blades when it's 100deg.