[jurialmunkey]

The service monitor will always run (unless the actual plugin is uninstalled/disabled) - what the SkinSetting does is tell the service monitor to idle and basically do nothing except occasionally check if the skinsetting was enabled.

So, this means that we don't need the Skin.SetBool(TMDbHelper.Service) anymore.

No you still need it. The setting is what switches the service from idle to active. i.e.
Skin.SetBool(TMDbHelper.Service) - Makes service active
Skin.Reset(TMDbHelper.Service) - Makes service idle
Skin.ToggleSetting(TMDbHelper.Service) - Toggles between active / idle

The useful thing about the setting is that you can toggle the service to be active only in the windows or sections where you need it (e.g. you could toggle it so that it is only active for Home.xml and MyVideoNav.xml)

The Window Property just tells you that the service started correctly:
Check if service started correctly:
!String.IsEmpty(Window(Home).Property(TMDbHelper.ServiceStarted))

Check if service started correctly and is active:
!String.IsEmpty(Window(Home).Property(TMDbHelper.ServiceStarted)) + Skin.HasSetting(TMDbHelper.Service)

Check if service started correctly and is idle:
!String.IsEmpty(Window(Home).Property(TMDbHelper.ServiceStarted)) + !Skin.HasSetting(TMDbHelper.Service)

Another one.... when you load the video info dialog for a movie the languages info it's the one that delays the most. Even if you load the dialog for a first time all the other infos are loaded instantly the languages info they need the double time to load. Sometimes the service monitor stops when all info are loaded and it starts again to fetch only the languages info. So i guess something is not working properly there.

This is what I was talking about with kodi setting/clearing properties in a separate background thread - my plugin thinks it has finished because all the commands have run but Kodi is still setting the properties in the background. There isn't any way for me to check if that background thread has finished - i.e. I send a setproperty command to Kodi core but I don't get any return signal to indicate whether it is finished. I can't check the property itself because it might be from a previous item (and clearing first causes more issues due to the threading).

1. The SetProperty(TMDbHelper.WidgetContainer, ID, Home) it's not working anymore. It's always empty.

Working fine for me. The service doesn't set this property - YOU need to set it in your skin. It tells the service what container ID you are using for a widget.
e.g. If your widget is <control type="list" id="19001"> then you need to set SetProperty(TMDbHelper.WidgetContainer,19001,Home) to tell the service that you want details for Container(19001).ListItem

BTW, the service will work in the info dialog for a widget even if the the property isn't set. You only need to set it if you want to display info alongside the widget on the home screen itself.

2. If you load the video info dialog in videos section (movies or tv shows) close it, exit to home screen, go back again to videos (movies or tv shows) and load the video info dialog again for the SAME ITEM.... then all the info are empty. You need to navigate to another item so the info from the service monitor to load.

Can confirm and reproduce. Should hopefully be fixed now.