Bad quality scissors will invariably suck for lefties because the grip of a left hand pushes the blades apart, vs. with a right it pulls them together. Scissors are my #1 gripe as a leftie too.
I use the mouse with my right because the rest of my family is right-handed so it was on the right and I just learnt by copying. I don't mind it, as I can type fairly reasonably one-handed with my left hand - much better than I could with my right - so it means I can still do short typing bursts one-handed without lifting my right hand off the mouse. When I type with two hands, I find my left covers about 60-70% of the keyboard vs. my right doing about 30-40% of the keyboard.
Funny - I’m right-handed, but my left hand also works most of the keyboard. I think it’s more because the modifier keys on the right are more natural for me to hit.
On thumb keyboards, it’s pretty similar too. My left thumb types as far to the right as U/G/B.
I use the mouse with my right because the rest of my family is right-handed so it was on the right and I just learnt by copying. I don't mind it, as I can type fairly reasonably one-handed with my left hand - much better than I could with my right - so it means I can still do short typing bursts one-handed without lifting my right hand off the mouse. When I type with two hands, I find my left covers about 60-70% of the keyboard vs. my right doing about 30-40% of the keyboard.