Upgrading from single site install to multisite install on same host

Hi All!

Well, the time has come for me to upgrade my single site install to a multisite install. Initially I had a single install because that was all that was available. Then I found out the host I was with, JustHost, did not support multisite. So I found a host that did and it will also grow with the business - TMD Hosting.

Two years in the making this website ... for the various keyword phrase searches it is no. 1 on Google WITHOUT content - awesome SEO :o) It is beating the government websites and big brands. Yey for me! This is even with an "Under Construction" landing page (someone was trying to pinch my ideas, concept and format, so I covered it up). The backend SEO is working a treat.

However, I am am unsure how to do this without losing my ranking. We will be launching in a few weeks as now I have a legal representative on board to protect the business. I didn't want people stealing original content and want to protect the artists I will be working with. you cannot see my site as it still has the "Under Construction" on it.

I have a few of reasons for converting to a multisite installation.

1. The AWESOME plugins that are available for multisite - peeved they are not available for single site installations.
2. I was approached by a broadcasting network and GIVEN a digital TV channel - so it will require its own website.
3. I can have the varying sites under one installation without having to keep switching between tabs/windows as a superadmin - hope I have this right.
4. I can install all the plugins on all websites in one hit (is that right?).
5. Simplify things a bit.

So, do I backup the website and download, take the whole thing off, reinstall with a multisite install and then load it back up again?

I think the main site, that was originally installed with JustHost when I joined (free website) is not the one I want to upload and it is redirected to another installation of wordpress (single site).

Hope this all makes sense. I really need to get moving on this ... and now I have foudn the template I was using is not available anymore and I have to change. Luckily I can do the site in one day again - but the ranking is what I am worried about.

By the way, I have the backup plugin installed. Wordpress Database Backup.

Hop you can tell me the process - or if there is any documentation on HOW to do this on WPMUDev? I think there would be a lot of members who could do with this info.

Cheers
Judie