Replacing all of the components is a recipe for turning a cheap old bike into an expensive old bike that has a few new parts.

My bet is that a good cleaning followed by new brake pads, cables and housings, and maybe tires, is all that bike probably needs. Of course, like Andrew Stewart said, I haven't seen the bike.

On those broken crankset teeth - take a close look at the teeth exactly opposite from the broken ones. If you see a set of similar teeth, that's a design feature for improving shifting.