Your advice is sadly very out of date.
Ram upgrades are currently only an option for the Mac Pro (trashcan), the 27" iMac, and (possible but not easy as you have to take the entire thing apart) the iMac Pro. Every other model of Mac now has soldered in place RAM.
The only Macs that still use SATA storage are the non-pro iMacs and the Mac Mini. AFAIK, every other Mac now uses proprietary pci-e SSD sticks. On the latest Macbook Pros, IIRC, the SSD is soldered onto the logic board (so data recovery from a dead system becomes a problem).
Basically, nowadays the smartest thing to do in most cases is to order your mac with the RAM and storage you will need for the life of the system. Especially if upgrading will require major disassembly - risking destroying your $2000+ computer in an attempt to save a few hundred bucks on an upgrade makes no sense at all.
