Hey fellow New Jersey resident: to add to what Goomba said, if you are competing for Time Trial times (http://www.mariokart64.com/mkdd/) we only use IGT as opposed to RTA.
Hey there! The current 1st place holder for Time Trials (and WR holder for every speed category), Goomba, has a very good series on YouTube called "Zero to Hero," where he goes through each track slowly, detailing what should be done if you want to get good times. You can also join the Double Dash discord server, people are always willing to help newcomers! https://discord.gg/zhzfxZg
Not to mention that no one even updates the meme leaderboards so they pretty much don't even exist.
Co-op is fun to do, it definitely does add to the game. I think it should be a category. Reee at me all you want, co-op is super fun to run and it's what got me into the game in the first place.
since I'm not allowed to edit the spreadsheet, I sent a request with the relevant info and a screenshot, could you take a look, please? :)
I recently did a co-op run with a friend, and we beat my solo PB: would it be okay to submit to the leaderboard or is that solely for solo runs?
I'm not sure if there is a difference, although even if there is I don't think it would matter due to the heavy RNG in many parts of the game. I'm a newcomer so I don't actually though, although that's my suspicion.
Hope this helps :)