I got my wallet in under 50 missions. It feels a lot of grinding, especially once I start getting to the iron door, but can't punch trough. Easiest way to do it is with the cruisers and investing in max speed, just get a cruiser before the door and you're set.
Bosses are have the AI of a rock. Armor doesn't seem to work for the best hull, in fact it makes you bigger and you die faster. Easier to use the first upgrade that is focused on armor, it is smaller than your original hull and probably gives some extra armor.