Using an adxl345 accelerometer to measure maximum force impact on a tackle sled

If you align the accelerometer with the axis you want to measure along then you can read the acceleration along that axis at regular intervals and remember the peak value.

I don't know whether you're planning to know the mass and coefficient of friction in advance. I don't see any way to determine them from the accelerometer data.

Given the formula you want to evaluate, it ought to be possible to implement that calculation in code.

Reading from an accelerometer, reading button presses, displaying text on an attached screen, are all things you will need to learn to do but they are all things that many other people have already done so you should have no trouble finding examples.