Installing Drupal

I've seen several examples of setting up a multi-site installation of Drupal, though we are looking for a scenario that seems to be different from what many are.

We'd like to have a single application/db/configuration that will allow multiple installs of drupal on different domains. Here's an example:

1. Core application site with highly configured content types/modules etc.
2. Separate instance on another domain (we have this figured out), with the same configuration, though the two instances do not share content.

So, I've installed Drupal in a subdirectory while building the site. When it's ready to go live, I can just transfer them directly to public_html and everything should be ok, right? Do I need to change something in the files?

I want to install Drupal on my webroot (www.platiniumglobalventures.com) and not a subdirectory (http://platiniumglobalventures.com/hp_drupal). What should I do???

I don't like the looks of my website, how can I upload d theme and module of my choice and edit them to my taste?

Moreso, I wonder why all these unnecessary post should be on the subdirectory I installed Drupal on
Unnecessary things like

Newbie using Drupal 7 under Ubuntu.

When I installed everything on my desktop, I fell into a single-site installation, probably from a combination of anxiety and laziness. Now that I am a few days away from making my first Drupal site live, I realize that since I'm probably going to be putting together at least a few more, I'd be best off making my desktop installation capable of handling more than one. So, I want to first set up my local machine to enable me to create more than one site, before I go live with the first one.

So I'm trying to put together a plan. Right now my drupal directory is located in /var/www, and I've been building example.com in /var/www/drupal/sites/default. The /files subdirectory there contains about a dozen subdirs (/ctools, /css_injector, etc.) as well as 20-30 PDFs and jpgs plus a .htaccess file.

The relevant part of my /etc/hosts is:

127.0.0.1 localhost
127.0.0.1 drupal

I gather that typically, a multisite installation will have the folders

drupal/sites/example1.com
drupal/sites/example2.com

Questions:

1) How will I have to make changes in the mySQL configuration for example1.com?

2) Can I *rename* .../drupal/sites/default to .../drupal/sites/example1.com? Or does sites/default have to be *copied* to /example1.com, and /sites/default left intact?

During configuration of my Drupal-installation the black admin-bar on top (Home Dashboard Content Structure...) suddenly disappeared and I can't get it back. Using drush I disabled almost every module but that didn't help me. Can anyone help me with this issue? I'm stuck...

I'm trying to install Drupal version 7.9 but can't progress pass this error during the installing process:

Failed to CREATE a test table on your database server with the command CREATE TABLE {drupal_install_test} (id int NULL). The server reports the following message: SQLSTATE[HY000]: General error: 27 Can't sync file './drupaldatabase/drupal_install_test.frm' to disk (Errcode: 122).

Why would I be getting an error that says it "Can't sync file"?