How to determine which Fouriers Series terms to use to approximate a signal?
Your inclination to choose the largest magnitude coeffecients is the correct one.  There is a Linear Algebra explanation for this having to do with orthogonaility.

However, your second question is more pertinent, I think.  If your sole motivation for reducing the coefficient count is to reduce data entry effort then you are much better off formatting the output of your DFT analysis as syntax for inputting into your code.  Then a simple copy and paste will do the job for you.  You also greatly reduce your exposure to data entry errors.  Depending on the volume, a custom programming solution which automates the copy and paste process might be economical.

Hope this helps.

Ced