Cactus baby OK?

I cut this stem from a moon cactus 2 weeks ago on Monday, July 15th. 2 questions:

1. I'm ready to plant it, but I noticed something strange on the top of one cutting. Is it OK? Pic 1-4.

2. Any advice for soil once I plant it? I'm assuming Cactus soil is OK? Pic#5 is the roots starting.

Please let me know if this is the right sub for this question.