Topsoil on top of rocky soil

Usual21

Last year I purchased my house that was completely surrounded by trees. We tore down a bunch of them and made a yard that circles the sides and the back of my house. The only problem is that the soil is filled with rocks and weeds. There are big rocks that are the size of a grapefruits.

This is what I thinking of doing. Could I rake out the biggest of the rocks and then just lay down about 4"-5" of top soil on top? Also, do I kill the weeds with weedkiller or pull them all? I'm hesitant about using weed killer since I want grass to grow eventually. Would this work? We want to put down some grass in the near future.

Also, what is the cost of topsoil? Sod is out of the picture due to price. We will be seeding ourselves.