The ability to deal with the rusty crust and to know how much effort it's going to take to sand it back to to metal stops me in my tracks (fear creeps in I gulp it down and look again). I know what it needs.
You need to fill the dents and prime it up. Give it a first thin coat so it doesn't show a drip and then a second (possibly a final third coat) so it ends finished in a lustrous deep colour of white.
Ah yes! when the flat creeps into a concentrated mess of layers and sub layers. The easy thing to do would be to sit paralysed and unable to take your finger out of the dyke for fear of drowning.
Boldly I learned one day from a friend the following: Go into the mess and pick one thing up. Ask yourself "were does this belong?" Take the item and put it away, if it had no 'home' then make it one.