If you want to start applying footsies, don’t be so complicated with all this subtle bullshit about trying to get whiff punishes etc.
Basically all footsies boils down to is you want to keep yourself spaced proportionally to your opponent in a way that you really like… or a way they really don’t like.
If they are playing Dhalsim, you want to keep them far away obviously. If you are Zangief then you want to spend your time in or close to throw range,
That’s footsies at it’s heart, put yourself where you think you have the best odds of winning. Expand upon this basic thought process into more complex things based on what the character does, but more importantly what your opponent does. Learn matchups, figure out your zones, etc. it can get as complicated as you want.
EDIT: don’t forget the classic shoto trap. Fireball to force them to jump, shoryuken to punish when they do.