You can knock the rust off pretty well with a green or blue Scotch Brite from any general store. They're about 600 and 1000 grit finishes respectively. #0000 copper or steel wool is good too. WD-40 and 3 in oil is barely ok, but the best oil for most things is clear mineral oil. It protects, but doesn't dry hard like 3 in 1 or WD-40 if the bar gets left for extended periods.
Bar should be fine, I've never seen a bar rust pitted to the point of being dangerous. Most bar breaks are bad drops, or people doing odd things like re-cutting the rings, etc....