The package turns out to be of the same size. Perhaps I am mistaken here. What do you think?
the two are hard linked
What's the use of those compressed source .el when we already have the .elc? Is it necessary to keep the .gz in the package (actually I leave them out in my emacs-lisp package) ?
emacs doesn't need the source .el (gzipped for saving space) to run.
The sources are usefull when you start learning elisp, and want to have a peak at the source to understand the functions better, or when you want to write a function that does slightly the same thing as an existing one.
So, you can put the .el.gz in an optional package, (debian does that for instance providing the .elc in the emacs package and the .el in a separate optional one), you should add the ones that are not byte compiled together with the .elc.
The fact that the .el also exist as .el.gz is probably because the build script gzip every .el files for simplicity.
One thing that you want to put in the base package is the etc/DOC-23.... file
it is required to get the documentation on a function defined in C.
(C-h f function RET)