How much cooking space does it have?

563 sq. in. total: 430 sq. in. on the primary grates plus a 133 sq. in. warming rack. That is enough for roughly 35 burgers at once.

What does the sear burner add over the main burners?

It is a dedicated 12,000 BTU burner for high heat, so you can sear steaks while the main burners run lower for other food. The side burner is separate and meant for sauces and sides.

Does it come with a propane tank?

No. The cabinet is sized to hold a standard propane cylinder, which you supply and connect yourself.

Is the stainless steel really rust-proof?

Stainless construction resists rust and cleans easily, but it is not rust-proof forever. Wipe it down and cover the grill between uses to keep it looking new.

How many people can it cook for?

With 430 sq. in. of primary grate and a warming rack, it suits a family or a backyard gathering of roughly a dozen or more, depending on what you grill.

Is a four-burner grill worth it over a three-burner?

The extra burner gives you a hotter sear zone and more room to move food between direct and indirect heat. If you regularly cook for a crowd or want steak searing, the fourth burner earns its space.