how many times do I have to install the stand alone manager?
Only once, if reinstalling sceneries using old installers. Never, if you install sceneries using their current installer.
I am installing all my sceneries again and everytime I load fsx after installing scenery AND the latest stand alone manger it tells me I have an outdated version.
The Addon Manager can't obviously say that is *itself* outdated...read that message more carefully: is surely telling you have an outdated version of the *scenery*
How may versions of the download manger are there?
Only one, of course. And it's always downloaded by the scenery installer online from the same place so, it's not possible to get an outdated version of the Addon Manager by mistake, unless you use an old version of the scenery installer AND you are installing without an internet connection working.
I have the latest one but fsx always tells me it's outdated. Can you shed some light on this?
No, it doesn't say that. The Addon Manager is probably saying you have an outdated *scenery* and it's also saying which one, so the solution is of course to download the current *scenery* installer, not the Addon Manager installer.