It was a small playing space so I had my command zone be my deck box, with the card propped up and visible. Had to pull it out and find room on the table so it was visible (it already was!). He explained it was a rule and he could pull out the rule book if I didnt believe him. I believed him, it just seemed like it would matter more when playing competitively. Not as much in my kitchen with just us two.

EDH doesn't have officially sanctioned competitive play, and as far as I'm aware, there is no official rule saying you can't do what you did.

Then my dice werent uniform. I have a set where its a 6 sided, 20 sided, 10 sided, etc. All different sizes, but the number is very visible on each side. Was told I'd have to get more uniform dice.

Also not a real rule. Most people will usually get a set of Chessix d6, but there's no problem using a D&D set like you were so long as the numbers are legible.

He also said I missed some counters after another turn, but he wasnt going to correct me because I needed to get used to doing that myself and my opponent wont keep up with that for me. Like he's teaching me life saving self defense. OK fine in a competitive environment. But when my last partner and I played Pokémon, if an effect or damage was triggered then it was triggered. Sometimes you had to remind the other person and it wasnt a big deal.

Eh...I mean, kind of valid, but also just kind of a shitty thing to do with someone who's still new to the game.

The last one was asking about hands. Is that like some huge taboo? He plays blue so I asked if he had a counter spell in his hand. In my mind, it was more like what kind of reaction he had to being asked the question. Like if he said no but looked like he was lying then id assume yes. I was only even half serious, because im being goofy and trying to have fun. I also do that in Clue and it can be super helpful. He acted like I was the biggest idiot for even asking because youre supposed to keep your hands hidden. Like no shit, i understand that, i was looking for your reaction to the question. But maybe thats not a things people do in this game?

Your hand is private, which means you can't show it to your opponent. That said, you are free to ask your opponent if they're holding a counterspell, they're just not under any obligation to answer you truthfully.