try copying your pkg somwhere under /usr/local/YourCompanyApps

Do I need this at the end or is this for an if statement to return if the install failed or not. exit 0 ## Success
exit 1 ## Failure

yes, you should keep that at the end of your script in Composer. You can use logic within your script to determine an exit code for instance: after the installer runs, you can capture the exit code from the installation using $?. exitcode=$?
if [ $exitcode -ne 0 ]; then
{ exit 1 }
else
{ exit 0 }
or something like:

installstatus=$?
[ $installstatus ! -eq 0 ] && exit 1

I end my install commands with -allowUntrusted

/usr/sbin/installer -pkg "$pathToPackage/SweetApp.pkg" -tgt / -allowUntrusted

If that helps