Hello,
What you are trying to do certainly is possible, but as @nirgrahamuk mentioned, the performance would depend on what type of Excel file you are planning to use for upload.
A great way to get started is experiment with the openxlsl package. You can read, style and write Excel files with that.
Depending on how complex the formatting of the input is (plain Excel table vs.lots of markup, formulas and macros) the processing and output might be more complicated, but in my experience reading form most Excel tables is really easy for R. The package comes with two vignettes to help you get started if you want to do more complex stuff.
Hope this helps,
PJ