You're gonna want to use the X or Y buttons to jump. Whatever shoulder you prefer, I think the usual is R for shield and L for wavedashing and L-cancelling. But I use L only for everything lol. It's personal preference.
Actually, I think it's the other way around; L for shield, R for wavedash is more common, due to SSB64 being only able to shield with your left index finger.
But ultimately doesn't matter. Just make sure that you do one with one finger and the other for wavedash. Just makes life simpler when you try and learn Wavedash out of Shield.
X/Y doesn't really matter, but Y is technically closer to all the other buttons, so use that, especially if you're gonna main Fox or Falco.
I don't agree that sliding is superior to simply tapping the button, but that's me; sliding techniques tend to put your finger even further away from buttons. >.> Again though, do what's comfortable. Short hop is all about letting go of the button/stick fast enough. Doesn't matter how light or hard you press. Just let go fast.
To get around counter, bait it or run in and grab. Or empty hop grab. Or randomly miss. lol I have a tendency of accidentally messing up as I try to attack, and end up whiffing my attack or barely missing them. Always drives one of my friends insane, cuz I only seem to mess up, when he tries to Counter with Marth. XD