They are called break-out-tabs or mouse-bites.
This is how this is done:
If I place them with the yellow line on the edge.cut there will be excess sticking out of the outline after breaking them apart (= needs filing). Setting them back, so that the blue line is sitting on the edge.cut (rightmost example in the screenshot) there is no excess sticking out - but on the board this naturally needs a bit more space (set back of components/tracks).
The footprints I use for the many drills are like this one:
z_Drill_05x10.kicad_mod (2.2 KB)
They work well on 1.6mm FR4.
2.0mm thick FR4 needs side cutters (or good nerves) - or better larger holes in those footprints.
I suggest flat pliers to snap them - just advance with the tip till you're right at the drill-line and then snap with the pliers. Without pliers the pcb bends as your fingers are 'soft' and you risk delamination or components breaking off if you do this after reflowing/soldering (as it's supposed to work).
A 3-4 hole one every 50 mm is more than adequate.
Oh, and milling cut widths I use are 1.0 mm for 1.6mm FR4 and 1.5 mm for 2.0mm FR4.
Some more reading: