1 added new guy cus I noticed 2 other threads basically with the same name without the new guy and I just made this account maybe like an hour to 30 minutes ago

2 I have a PS2,ps3,ps4, 3Ds, the switch also I use steam quite a bit.

3 could I speed run a ds game on the 3ds or does that not count cus emulation?

Playing a DS game on a 3DS isn't considered emulation. Just note it somewhere in the description that you played on a 3DS in case there are differences in load times.

What about remakes? I notice super mario 64 is very popular (well sorta daaa but still) Would playing that on it's remake count? Or does the remake have it's own page?

There's a page for SM64DS that's separate from the regular SM64 page. https://www.speedrun.com/sm64ds vs https://www.speedrun.com/sm64

As for perfences for games, shorter games to speed run that wouldn't take more the half an hour to attempt at a time.