Order of unlocks
1. first you want to unlock the permanent souls bonus twice this gives you a +2% chance for souls to drop. the reason is it’s going to make everything else quicker.
2. You will want to unlock the stability perk at least once because using the method I will describe below requires it to make it to the late game.
3. You are going to want to unlock the Uncommon hat because this will make the game only provide uncommon upgrades when worn, this is not the ‘best’ hat in the game as that is subjective but ti does make for the quickest farming do to the ability to upgrade your fire rate very quickly the side effect is you won’t be able to give stability to your shots so this is why you need the perk for it at least once to survive longer.
4. Unlock the trident because it offers the most defense do to it’s three shots being able to stop enemy bullets in multiple directions as well as bullets focused at the center of it’s shot.
As far as cards go you want to get at least rate of fire buffs as soon as you can and disregard even damage unless that is all that is offered, ideally you are trying to get so much rate of fire as you can to block enemy bullets.
Using this method you will farm 50 souls in a single run on the regular.