Hey SorcereesGameLab, a couple of your questions are already answered in the quick overview:
Quick Licence Overview:
-You CAN use the assets in commercial and free projects.
-You CAN edit and repurpose the assets.
-You MUSTN'T redistribute / resell the assets.
-You MUSTN'T use the assets in any printed media or physical product.
in the first pages of the licence there are also FAQ questions, hopefully answering every possible question you have quickly and clearly. If something shouldn't be covered ask away =)
Cyangmou's Itch.io Licence Agreement
Giving Credit is not a necessity, but appreciated =)
Thanks.