What you want is rather ‘electronic design question’ than ‘KiCad use problems question’. In past I sometimes get into such discussions here but later found it is not welcome. Forum mainteiners want it to be good place for people searching solutions with KiCad software use so as much as possible it should not be cluttered with other discussions. Good place for electronic questions is probably EEVblog.
With your design several separate discussions could arise, like:
- how to ESD protect keyboard,
- how to protect your circuit against other external disturbances,
- why you should add GND plane to your PCB and why it should be continuous,
- what for are decoupling capacitors (and where and why to place them),
- what supply regulator to use (if low-drop than how to ensure it being stable),
- do you have to use filter at supply,
- what you plan to do with read keys (external interface?).
All of them are electronic, and not KiCad related.
If you want to learn about PCB design I recommend articles I mentioned here 4 years ago: