If you are going to sand, only do it where there are areas of porcelain missing.
Personally, I'd use SOS pads or 0000 steel wool and no sanding.
Highly doubtful there is rust on the inside. It's probably dried up cooked on gunk. Oven cleaner or a razor blade or elbow grease are your best bets for cleaning that off.
As far as rust on the outside, I have found treating it with flax oil to be very effective.
Best of luck.
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