Is there a walkthrough for what to do differently for all endings? Maybe even a hint at all the day/times that I could load close to the branching paths?
Yes.
To get the 75% ending:
-Say yes to all yes/no prompts.
-Hack the CAOS ship in the hangar. (To do this, access the menu in the bridge and choose "remove locks" after using a bio-explosion to blast the door off.
-Grab the data disk when priming up the gate in the control room.
To get the 100% ending:
Edit: Make sure you also collect the override chip from your cyborg leg after transformation into a alien-human hybrid.
-Do everything above.
-This time, when you receive the message "Help..Ka.." after the boss battle, go back to the area where you killed the monster with the machete. Then, interact with it, and continue the game as usual. You will unlock the last ending.