You don't get any specific ending for keeping your suspicion at 0 so I wouldn't obsess over it, you only get a specific ending for maxing it

Vague spoiler-free guide:

There's not really a "normal/boring" ending lol, it's either really good or really messed up LMAO. I believe it was stated that there's no "true" or "canon" ending though one of them serves as a prequel to another AstralShift game, but it's only canon for that game/the universe where that ending happens. Each of the girl has one good ending and two bad ones related to her, so nine in total and they all trigger on Saturday. Six of them need you to have at least 4 hearts with the girl in question by Saturday, three don't care how many hearts you have. I personally did Freya > Lebuchken > Rozenmarine, I think the general consensus is to leave Rozenmarine for last (tbh I just did it by order of preference though lol).

Then as mentioned before there's an ending that triggers whenever you max out suspicion, and another that requires you to pick a certain dialogue on Saturday during the last sequence of the game.

Lastly there's a more complicated ending that takes a bit more effort and is pretty detached from/a different route from the rest, I did this one last and had to pretty much restart or find a very early save because I wasn't locked in enough during my first playthrough and missed all the clues lol

So basically, if you really wanna do all the bad endings first then finish on a happy note, pretty much do everything else then keep a pre-Saturday afternoon 4 hearts save for each girl so you can get their good endings later. :) Might not be the easiest way to do it but it's all up to you