Landing deceleration - help me with product design

[OrryFace]

Hi clever chaps,
No, I'm not a driver but I have had a long career in encouraging freight to self load (otherwise known as passenger marketing).

I need some help with understanding the physics of take-off and landing in order to develop a component switch which would use either an accelerometer or air pressure sensor to automatically detect the status of the aircraft.

So my questions are -
a) is there an absolute minimum acceleration below which a commercial aircraft cannot physically take-off...and an absolute minimum deceleration once the wheels hit the tarmac ?

b) likewise with cabin air pressure. Or are these modern aircraft so sophisticated that some can land and take-off with inperceptible air pressure change?

thanks,

OF