Q2: Same way as double-click people. A file only opens if I click, not when I press the mouse button and drag the file around.
Q3: I draw a small selection frame over it, or press the control key when clicking (I have the hand there any, especially if my next input will be Ctrl+C/X and Ctrl+V
Q4: I just do. Sometimes I relax by playing shooters with the “invert mouse” option turned on :D
I have never had a cell phone or smart phone in my life, single-click was the default when I switched to Linux, I gave it a try and I liked it.