Welcome to SRK.
-holding an arcade stick
Please read the stickies before asking questions.
I wouldn’t worry too much about how Daigo and whoever else holds an arcade stick. As long as you can hit all the directions comfortably and you aren’t causing hand/arm strain, you’re probably fine. You can probably google up some info on “daigo grips” and whatnot, but it most likely you’re better off spending your time in training mode instead. Players don’t usually spend time talking about stick grip like a golfer would.
Stopping when you hear a click is generally more efficient. There are times when riding the gate may “feel” better, e.g. SF4 crouching dragon punch shortcuts, charge specials, etc. ymmv
Spam is a term that generally sets off scrub alarms in the competitive community. It implies you’re doing something over and over again mindlessly.
-how to throw fireballs as fast as possible
Generally in street fighter games, you can only have one projectile on the screen at once. If you are doing the motion correctly and not getting a fireball, there is either already a fireball on screen, or you are in a state where you can’t throw one, e.g. dizzy, knocked down, being hit, etc.
Shortcuts are fine, but know that shortcuts for some games don’t always work in others.
If you’re asking whether you can input 3 fireballs at once and wait for them to all come out, no.
Mike Ross is a palm player too, so if you want to get good stop that (just kidding).
In terms of fireballs not coming out:
Do you make sure that the first fireball has vanished from the screen completely before you throw another?
Generally with fireball characters, they can only have 1 fireball on the screen at a time, with very few exceptions.