i have done all the steps of editing my sequence and saved metadata the final time.

BUT

why do the tutorial recommend me to render from the library tab instead of rendering from lightroom directly?
i have downloaded a script that allows me to render movies directly from LR without having to render everything as images first.

It recommends to render with the Lightroom Export Plugin "LRTExport", you'll find it when you hit "Export" from the Library Module in Lightroom.
There is no way to export High Resolution video directly from Lightroom since Lightroom version 5.

hmm, i adownloaded a plugin that allows me to render everything from small 480x to 1080 videos.

just think it takes double the time to first render images to a new folder and THEN render the video itself

Any plugin will have to export (=develop) the images first, there is no way around it.
Using the LRTExport plugin is best practice for time lapse, and will deliver outstanding quality. There is no other solution for Lightroom that is faster and delivers the same quality.

BTW: What's the name of that Plugin? If it uses the slideshow module, the quality will be rather weak (adobe's limitation)

Any plugin will have to export (=develop) the images first, there is no way around it.
Using the LRTExport plugin is best practice for time lapse, and will deliver outstanding quality. There is no other solution for Lightroom that is faster and delivers the same quality.

BTW: What's the name of that Plugin? If it uses the slideshow module, the quality will be rather weak (adobe's limitation)

Here's the URL for the Plugin/script
http://lightroom-blog.com/presets

Then lrtimelapse. 

That's what I use.

Whit this I just press export, name the file and resolution and that's it, I will be happy to try out your method as well.
And that basically means I render first the images, and then choose that new developed folder from your application and choose render video again and get the final result?