I don't know about anyone else but I usually put them in the sockets that are there...

44s work as do 47s, 47s have a bit less amps which equals a bit less heat build-up

Schematics will sometimes specify a flasher. You've already found the concave cutouts. Other than that personal preference

People get wound up over the heat from 44s but in home use it is simply not an issue unless you just leave games on for some reason.

Absolutely

Flashers are generally 455s

44/47 pretty much everywhere. Occasionally the schematic will specify a flashing bulb in the backbox, but not always. And as you've noted sometimes the socket area in the backbox will be concave for a flashing bulb. Aside from that it is really a matter of preference how blinky the owner/operator wants the backbox to be.

I like to refer to them as blinkers, because the bulbs themselves are designed to provide the blinking. This is in contrast to "flashers" in the solid state world where the CPU sends a brief pulse to special lamps to accomplish the flash effect. When one says "flasher" most picture the solid state flashlamps and CPU pulses.

Here is a sample from Gottlieb Mini Cycle:
Capture (resized).PNG

"Pinball Soul" - that was the name of a great pinball podcast a while back.

Credit to bintzknocker who shared in another thread. I now have an erupting volcano. Look for the socket that is mounted different than the others. For gottlieb at least.