A brief note - MedPAC updates its roster of 20 PDF chapters about each of the CMS payment systems.
https://www.medpac.gov/document-type/payment-basic/
These are concise - for example, the lab reimbursement summary doesn't cover a lot of its details. However, if you need an intro to a CMS payment system you don't already work in, these 20 entry points can be a good place to start. Plus, it's a testament to the fact that there ARE twenty separate, largely unlinked payment systems (DME, physicians, ESRD, and so on).