And I will be a good adivce to download the latest Addon Manager from FSDT Homepage ?
Obvisouly yes, since you are going to install without an internet connection. This way, you'll get its latest version in any case, since the files embedded in the installer will be the same that you would get online.
Is it o.k. to install for FS9 the latest Addon Manager above the existing one on my system, also cloud 9 Amsterdam, KLAX and FSDT KJFK are just installed?
If you think your Addon Manager needs be to updated, as clearly indicated on the website, there are no problems installing over exising sceneries.
Or is it necessary to uninstall all this older sceneries installing new Addon Manager and then then sceneries in a chronological order new (and activate all ones new...) ? I ´ll be more glad if not necessary.
The advice on FSDT Homepage is not so clear for me, at all.
The FSDT home page doesn't say you need to Uninstall, which means there's no need to Uninstall. If there was any need to Uninstall, the web page would have said so.
Also, depending how old your Cloud9 installer is, you might or not need to download the full scenery installer as well. But you will see a clear warning message in FS9 or FSX about which sceneries needs to be updated, if this is the case.
The chronological order doesn't matter. But, as explained on the website, if you installed a Cloud9 scenery that doesn't have an FSDT installer, it's best to install the Stand-Alone Addon Manager at the end.
Basically, if you always install the stand-alone Addon Manager as the last thing you do, you can't go wrong.