1) A character who I can relate to helps-- but mostly I want it to be a character who has positives and negatives. Ideally, a slice of life is extremely personal and therefore we get to see and maybe hear a lot of the protagonist's real feelings and it feels more relatable and realistic if not all of those feelings are always positive. The character can be really different from me, but if I can understand their motivations, their fears, their wants, etc, it's easy to become invested.
2) D-Does slice of life usually have opponents or villains? I don't think most of them even have antagonists? Maybe you're thinking of a different genre? Ideally, in a slice of life, LIFE is just the thing the protagonist and the characters are dealing with and not necessarily some big baddie or force. At least that's how I think of it. If the characters are gonna suddenly bust into action, it's no longer a slice of life, at least not what I think of it as-- and I'd probably lose interest.
3) I'm heavily invested in character dynamics and motivations. I am invested in a story when characters feel complex and actions feel tense. When I really, REALLY wanna see the next part due to the characters, I know I'm hooked.
4) I'm uh, I'm non-binary so? This really depends? Ideally, you wouldn't see much difference in female and male characters unless they're dealing with societal stuff? So, this one I'm just gonna leave up to 50/50. Really just depends on the story and what's happening. Odd question, imo.
Good luck!