Setting up a Blogging Website Portal

Hi everyone,
I’m trying to setup a self-serving blogging website where users can register and create their own free blogging site, but after installing WordPress as a multisite environment I’ve come up against a few problems (or limitations) and I would greatly appreciate any advice to find out if what I’m trying to do is indeed possible.

I’ve completed the WordPress multisite installation and configured the main website (http://www.website.com) with subdomains so new registrants to the main site can register a subdomain at for example (http://subdomain1.website.com and http://subdomain2.website.com etc) but after spending many hours reading through these forums, I think I’ve found a few problems that I’m having some difficulty resolving.

1. Having initially set my account up as the ‘Super Admin’ my intention was to automatically assign new registrants the ‘Admin’ role, similar to how they would if they created their own single WordPress blog at their own URL, but the highest permissions role I seem to be able to allocate is that of ‘Editor’ – is that correct or am I doing something wrong?

2. Because of the limitation as described above with the permissions, I can’t find a way to allow each individual blog user to be able to ‘Add New Plugins’ – the most I seem to be able to achieve is if I install plugins as the Super Admin and activate each as a Network Activation, this allows the individual blog user to Activate or Deactivate those particular plugins. This seems really odd to me because according to the many posts I’ve read in these forums, the multisite environment should work in exactly the same way as a user on http://www.wordpress.com, and they have full access to install and uninstall plugins of their choice. How can an individual blog user expand the capabilities of their blog without being able to install plugins that adapt their blog to their own needs?

3. This next problem may be just me and the way I’m accessing the sites, but if I’m logged into the Dashboard as the Super Admin and then open up a new browser window and create a new account on the site and register a new subdomain, if I then log into that account with the new details, the Dashboard still displays the Super Admin panel at the top – is this happening just because I’m also logged in as the Super Admin from the same PC or would this happen if someone on the other side of the world created a new account while I was also logged into the site as the Super Admin. Probably a silly question but I just need to clarity on this as it came as a bit of a shock when I discovered what was happening.

4. My final problem relates to Themes, my intention is to configure each new subdomain with the TwentyTen Theme as default and allow the user to browse the library of other free Themes to install as they wish, but I would also like to offer Premium Themes to buy through the main website – I’ve uploaded a large number of Premium Themes through FTP and I can see those if I click Themes in the Super Admin panel, I can also allocate one or more of those themes to individual sites by clicking Sites > Edit (subdomain) > and putting a tick in the Theme box to mark it as Active. My question though is this, and I do have some confusion after reading other forum posts: when that user activates the premium theme, if they play around with the CSS settings or make other code changes, will that effect just that theme on their subdomain, or will those changes reflect to other users of the site who also happen to use that same theme? This could potentially be a major headache and I’m not really sure how to resolve it if that is the case.

Sorry for the long-winded questions but I have scanned the forums for the last few days in the hope of answering these questions, but so far without much success.

Any help, suggestions or pointers therefore that anyone can offer would be incredibly generous and very much appreciated.

Many thanks in advance
Wayne