Help understanding practical transistor considerations?
Welcome to the real world of EE. A lot of what we do is from experience grounded on the solid theoretical teachings.

As you suspect in your first point, job number one is to nail down EXACTLY what you want your circuit to do including what tolerances you can accept. Having that knowledge in hand gives you a chance to select appropriate technologies and design your circuits to potentially conform to your specification.

Whenever possible use simulation tools to verify that the circuits do indeed do what you expect and ultimately build prototypes and verify it in reality. When necessary change or improve your design as appropriate.

When it comes to selecting particular parts it can indeed be a lot of balls to juggle. Sometimes it is easy, there may only be one part that does the job, other times the choices are so wide you need to find one that functionally works to your requirement and is acceptable in cost etc. and just go with it.

As for the more extreme characteristics. The thing here is to recognize when you are heading into dragon territory. Then spend the extra time on those areas, and or get help from a more experienced designer.