Hi there! Thank you so much, I'm glad you're enjoying it! To answer your questions:
1) In a way, they may have mechanical benefits: "Finished projects may grant you +1d6 when you perform a task while they are available and relevant. Make sure you take them with you (if you can) on your next journey." (p. 63)
2) Correct! "Advancing" is essentially becoming a better version of yourself. The points are an abstraction of how much you dedicate yourself to that activity.
3) Perfectly put! No way to remove taint; you live with the marks of your adventures for as long as you decide to keep going.
Hope that helps, and let me know if you have further questions!