Now I will answer your questions.

1. Make the number of steps 1 and the End Time 10 seconds, make the Time Step 5e-4 seconds.

2. Acceleration applies to all bodies everywhere. There is no need to pick anything except one surface to point the acceleration vector. That is the Z-axis. Pick any surface for that.

3. If you put the data into matlab and do an FFT, you will get the frequency content in the data. There will be a big spike at the first natural frequency from the modal analysis, or near to there for the nonlinear case. That is not Frequency Response Function, which is a ratio of input to output.

4. You would have to try the transient structural both ways: fixed+tabular acceleration or fixed rotation+tabular displacement support. Note that you have to double integrate the acceleration signal to have a different table for the displacement.