wow, that's a lot of Qs
can i cherry pick some?
yes, you can run the installer more than once. normally you run it once, then delete the installation directory (so that Joomla runs, instead of the installer from your URL) and if you want to tweak things later, you use Global Configuration or configuration.php
Depends which version of cpanel you are running, but yes, it kinda does upload one at a time. It will upload and extract from a zip or tar.gz though.
Not familiar with MySQL browser, but Cpanel's PHPMyAdmin allows you direct access to modify your database. This is a way to upload MySQL schema and data, yes.
Creates a database by prepending your username to avoid db name duplication between accounts.
You can upload Joomla as a post-installation version. You can load it from (a) Fantastico or (b) using the Joomla installer or (c) file by file from FTP. It should all work.
I managed to get through the Database Configuration stage by creating the database in MySQL Account Maintenance and then creating the user "sunspot_sunspot" (everything prefixed with "sunspot_" it seems) and then enabling all privileges for that user. Was it necessary to do that or should the Joomla Web Installer have been able to do it itself?
That is the correct way. Joomla cant create a db on your hosting account.
hope some of that is useful.
i will leave others to chip in on the other Qs
good luck with your site.