Let’s talk buttons. The 6mm button is the classic button. It comes in surface mount and through hole versions.
The 6mm surface mount button, DTSM-6 seems to be one package name, has nice beginner-friendly pads that are easy to solder. It comes in a pick and place friendly reel, but it must exceed the specs of most machines. On the Logic Sniffer we noticed that the 6mm SMD buttons were hand-soldered, and SparkFun, Seeed, and Adafruit all use a smaller button in their designs.
A 5.2mm button (or 4.8mm, or many similar sizes) seems way more common in pick and place assembled designs. The smaller size and lower profile must be better for automated assembly, but they are more slightly more expensive.
Footprints for both bottom types are in the Dangerous Prototypes Eagle parts library.