When I was a dumb teenager, I was part of a high quality scanlation group and learned a lot about typesetting. I know you said it's not a matter of choosing, but I'm just gonna summarise everything I learned just in case someone (and maybe you even) can use the info
One of the group's rules was to use fixed fonts for the following types of text:
Narration (straight and sharp-edged), for example Agency FB
Normal speech bubbles, usually all caps, most like to use WildWords but I'm not sure if it's free for commercial use, I'm using Action Man instead.
Shouting speech bubbles (sharp-edged text), Deathrattle BB
Small text (text on sides of speech bubbles that are read like an after thought) and quieter SFX, augie for me
Loud/sudden SFX, most like to use badaboom BB, me too
I'm still a beginner at choosing my own fonts and not entirely satisfied either but content with this enough for now.
Text placement, size:
Always centered in speech bubbles, diamond shaped if possible (e.g. 2 words, 3, 2 again)
Try to use the same/similar font size unless the situation requires it (e.g. really loud shouting). Otherwise it might become too hectic/tiring for the reader.
Varied according to speech.
Normal: oval bubbles
Unsure/quavering voice: swaying lines
Shouting: zigzag lines
Phone calls: rectangles
Thought bubbles: depends, some like dotted bubbles, others just use a light grey for them or those focus lines
Use borders when sound effects cover artwork, place and shape them according to the noise.
When there are several similar noises, you can vary the sizes to simulate a sound that becomes louder or quieter for example.
Ehm, I just realised I'm making a whole effing tutorial without anyone even asking for it
Sorry, I've got this weird thing where I have to overshare all the info I have in case someone could need it.
ANYWAY, searching for scanlation tips might give you some good inspiration as well. There are lots of groups who speak in forums about it.
Walter Ostlie also made a video about lettering: https://www.youtube.com/watch?v=LjwFFQlP5OM
Okay, gonna shut up now. Sorry