I guess you are installing OpenACS using the debian packages (nice!), so the only file you should need to edit is /etc/aolserver4/conf.d/openacs.sh, and all other changes should be done vía debconf.
If you are sure that the postgresql installation is correct, my advice is to purge the openacs package, drop the database, check if the www-data user has permission to access postgresql (have a look at /usr/share/doc/openacs/README.Debian) and reinstall the package.
It should work, and start an OpenACS instance at localhost:8000 (by default). If it doesn't, please let us know.