For the basics, sure. But there are still spells and class abilities that I don't know off the top of my head. I'll look things up after the game if I remember to do so.
I'll look things up then and there if I have to, as will the player(s).
You're a lot more iron-clad on the "once a decision is made it's done" than I am. I'll make the best decision I can in the moment but I'm not going to spend a lot of time at it during the session unless it's a critical turning point. If I made a mistake we'll just do it correctly in the future.
Problem there is that the "mistake" has in fact happened in the fiction, and a player has an ironclad can't lose argument to have that same thing work the same way next time.
As the campaign goes on and these things get hammered out, such in-session rules discussions tend IME to become
a lot less common. For me now, most of the rules debates are around things that haven't happened yet but that we can see coming e.g. rulings and clarifications for spells of level beyond what the PCs can currently cast, and those discussions tend to happen between sessions by email.
Personally I don't want to play a campaign with an evil PC - and I do mean a PC that is truly evil and acts like one, not just "I was evil in the past and now I'm trying to redeem myself." Different people play for different reasons, but I know that most of the people don't want and evil PC in the party either.
Just like it's not the DM's place to tell me how to play my character, nor is it the place of another player to do so. Not out-of-character, anyway.
In-character, however, anything goes. If your character has a beef with mine in the fiction then fine, let's throw down and settle it. Roll initiative and bring it on.
Your character can still do whatever they want but if you cross the line and I will let you know you are crossing a line your PC becomes an NPC. That may well mean I'm not the DM for you, but when it comes to what the characters do if it's not harmful to another player at the table I don't care.
So a character stealing from random NPCs is fine but the same character stealing from other PCs is not?
Yeah, no; not gonna fly. Why not? Because this runs directly afoul of my position that PCs and NPCs in the setting are - and should be treated as - the same.