Hello and thanks for the questions! I'll do my best to answer them :)
1) No, players must move up through the dice. This represents them gaining training in the given ability. Dice move from d4 to d6 to d8 to d12 (there is no d10, which is where the confusion might have come in?)
2) The intent behind that is to give players a conundrum :) Do they choose to make unlocking new Skills easier by making Checks harder to achieve (a lower dice makes more difficult tasks harder), or do they choose to make Checks easier by upgrading their dice, making them more generally capable out in the world, but make Skills harder to unlock. A specific design choice in this case! :)
I hope that answers your questions! If there's anything else I can help with, just let me know. And don't forget, Mappa Mundi is now live on Kickstarter, and the most up to date version of the rules (the Quickstart Guide) is available on the KS page.