DO NOT seal the tank unless it leaking. Putting sealer in a non leaking tank is like wiping before you poop.
I would not worry about that small amount of rust you have but f you want to clean it up in very short order go to your local farm and feed store and get a gallon of milkstone remove. Dump the gallon in the tank then top the tank up with hot water. Within a few hours all the rust will be gone and for a lot less $$ than Metal Restore. Drain the tank rinse out with hot water then dump in a quart of high proof rubbing alcohol or HEET and swish it around to help get out the remain water.
Millstone remover will remove heavy rust in around 24 hours. So for light rust less time is needed.