Hello, I would like to start speedrunning on Céleste and I wanted to know if the switch is suitable for that, which controller to use for maximum comfort, and some more info if you have it .
Thank you

Hello, running on switch is doable, but running on pc is much better since you can use modded celeste to have save states in game and so you would be able to practice much more efficiently.
For the controller I would suggest using one with a good Dpad, I like Ps3/4 controllers but other players play with all sort of them.
For general advices:
1) remove screen shake
2) map your controls in a confortable way. You want a second jump button and a crouch dash button in addition to normal jump grab and dash, and in general you want to be able to press any combination of those buttons confortably.

if you're on pc, playing on keyboard is also an option

this video is a good place to start, you can also find runs of a similar time you want to achieve and try and execute similar strats

https://www.youtube.com/playlist?list=PLik0hR4RgeYRQEpW_j6Bi57WRSsc6pEZG This playlist has some really useful skips and tips in it. Good luck