The answer to this question might have changed since it was first asked nine years ago: a book is now available whose goal it is to give a detailed elaboration on Freedman's work:

[*The Disc Embedding Theorem*](https://global.oup.com/academic/product/the-disc-embedding-theorem-9780198841319?cc=de&lang=en&), ed. Behrens, Kalmar, Kim, Powell, Ray (Oxford University Press, 2021).