It turned out that PHP did not have simplexml_load_file() installed. I ran
apt-get install php7.0-simplexml
Restarted apache and hosed the install in /plugins as well as its database, started over and now it has installed.
First of all welcome to CiviCRM :)
As CiviCRM is published under the free GNU AGPL license there are no licensing costs and you do not even have to sign up. All your grasrootgroups can use your database or get their own copy /environment of CiviCRM (depending on your use case / requirements).
Neither PHP 7.3 nor MySQL 8.0 are currently supported. Looking at system requirements I see a minimum but not maximum version of MySQL; that needs correcting. PHP 7.3 generally works but it's not part of the automated testing matrix as of now.
If Drupal you need to update the temporary files folder under Administer - Configuration - File System, and possibly in the files table you might have paths using a backslash that need to be converted.
Also even for non-drupal for the windows to linux direction pay attention to capitalization for any file paths. Linux is case-sensitive but windows is not.
For a clean CiviCRM reinstall under Ubuntu / LAMP / Wordpress to work, the initial clearing of all CiviCRM related files is essential. If there are any vestiges of a prior installation left, the reinstall will certainly fail (either with an Initialization error, or the "You do not have sufficient permissions..." error).
Here are the necessary steps to ...
I would recommend to get the CiviCRM package from sourceforge, the link is here:
Also please make sure to follow the installation instruction detailed here for installing CiviCRM in wordpress CMS.
I installed WP 4.7.4 and civi 4.7.18 on local and it got installed smoothly, yes it do gives notifications that you mentioned but that's expected:
Cron Not ...
This really looks like you're trying to install on a hosting provider, but you downloaded the WordPress package for Windows. I can see how this might have happened given the WP site, but it's not at all what you wanted.
Which hosting provider are you using? Do they offer WHM/cPanel? Or Plesk? These are management frameworks for hosting providers. Inside ...
You can remove civicrm.settings.php and run the installer again. Here's where to find it:
Note that this will NOT remove the old tables from your existing database. To do that, see here.