That grate looks totally fine. That little bit of rust should come right off.
You could probably just use a well used grate brush, you know one that's all covered in grease, just give it a good scrapping and the brush should remove the rust and recoat with grease/oil at the same time.
If you find the rust is a little bit more than just surface rust, or your wife insists, a light sanding and then recoat with oil (I prefer bacon grease) and you should be good to go. If you want to take the whole thing down to clean, and then recoat that'll take a little more work, but it can be done.
I've had grates that were totally covered in rust like the few little spots you have. After a good cleaning and a couple of cooks, they're grate!
Im with Craig in liking to keep all the original parts with the grill. Can't wait to see this one all restored and cooking. Let us know if you have any questions, we'll get you there!