How to replace Mac OS X utilities with GNU core utilities

While you can shove libraries anywhere you want, and use OS X very similarly to Linux, I suspect you are after information on "the OS X way" of doing things, in which case:

Your question is too broad. While similar in some ways, there are many fundamental differences than between software packaging on OS X and something like Ubuntu - well beyond "stuff goes here on Linux, and here on OS X".

For example, libraries typically live in "bundles" rather than folders like in /usr/lib - either as .Framework bundles which live in /Library/Frameworks or ~/Library/Frameworks (the framework bundles include headers, support versioning etc). Or shared libraries may live in application bundles... etc - each of these is a big topic by itself.

Without a more specific question, any answer shorter than a small book may not be very informative..

This article explains some of the basic locations, and their Linux-equivalents

Apple's documentation on this kind of stuff is extensive (e.g the intro to Frameworks)

The proposed find based solution takes about 5 seconds to execute on my system. The following bash snippet executes in a fraction of a second.

if type brew &>/dev/null; then
  HOMEBREW_PREFIX=$(brew --prefix)
  # gnubin; gnuman
  for d in ${HOMEBREW_PREFIX}/opt/*/libexec/gnubin; do export PATH=$d:$PATH; done
  # I actually like that man grep gives the BSD grep man page
  #for d in ${HOMEBREW_PREFIX}/opt/*/libexec/gnuman; do export MANPATH=$d:$MANPATH; done
fi