Without wanting to sound silly, "clever" or sarcastic … the answer to most of your questions could be yes, no or maybe, depending on other factors
In relation to developer … it's not a black-and-white answer, (pun intended).
Different developers can give varying results depending, to a degree, on which paper or film they are being used with and/or what dilution is being used.
Fine grain, high acutance, extended shadow detail etc. etc. are all (claimed to be) achievable under different circumstances … it can be down to the photographer to expose his film with view to exploiting these factors in the darkroom.
Don't bother with "articles or videos", these only reflect the thoughts of the person producing them and the results they've been satisfied (or dissatisfied) with.
Get the manufacturers' data sheets and work from there to produce the results you want.
In my experience, (some while past, now), fixer for film is usually prepared at a concentration to allow it to be reused several times, whereas even the same fixer, if used for paper, may be diluted differently with view to single-session use.
In either scenario, there will be a defined area of material capable of being processed for a given quantity of fixer.
Going beyond these recommendations will likely result in incomplete fixing, the resultant film/print may "look OK" initially, but, over time, will deteriorate
Part-used fixer is easily stored and requires no special consideration other can keeping careful notes of usage.
Similarly with developer. Some are designed for "one-shot" use and some for re-use with further consideration ie. second and subsequent films will usually require extended development times, so careful notes need to be kept.
Also part-used developer has a relatively limited shelf life. It'll need to be stored in an air-free container (squeezy bottle) and refrigerated for best results.
Paper developer, in my experience, is usually discarded after each session.
So, no cut and dried answer
Enjoy!
Afterthought :-
Remember, the shutter in your probably now aged camera, whilst consistent, may well be out of calibration, so if you end up with unexpectedly "thin" or dense negatives, it could be the camera causing the issue, not your processing