I got to 1350 souls at the end of day 10
Well at this point I had collected quite a lot of different pieces and bought lots of cards.
I had one queen with judgement (souls from kills) and world (more moves) and another with high priestess (give moves) and world (more moves). The rest of the starting board was filled with pieces with as many card slots filled with fool cards. I never moved these pieces unless absolutely necessary. And of course I maxed out each pieces slots with emperor cards.
I declined every single event and received more and more souls each time. At the end of turn 10 I sacrificed all my pieces. -> 1350 souls
I feel like 500 souls felt like an achievement but then it got quite easy to reach. 1000 souls is more like an achievement because then you can basically clear out the shop. Maybe everything in the shop should be more expensive? I think a tarot card could cost like 50 souls but then again early game would feel so slow.