Not totally your answer but a start to do some searches are see who works with API
Download the Excel File and look under the API and or Macro Search returns, the information that is in the Excel File is from this forum, so the Search Term use will return anything within the body of the Thread or Reply. Using Excel you can now use the Search or Find feature to narrow down the Search Returns. One major thing is most people don't know how to form a question so some good posts get lost etc..
Which .dll / namespace is the right one when i'm just trying to crawl throught the object tree of SW and gather some information like componentreference e.t.c?
SolidWorks.Interop.SldWorks is the namespace. Contains API objects. Looked at the IFeatureManager. You can access that from the IModelDoc interface. You find this in the API/redist folder in the soliworks installation folder. If you're going to develop an application for .NET 2.0 or 3.0 (up to framework 3.5), you shoud look for the same dll in a folder called CLR2 inside Redist. This should work with SW 2013 and older.
Do i have to have the full solid works software installed on my local pc to run such a stand alone application that utilizes the dlls?
Yes. SOLIDWORKS interops are merely interfaces that point to the SOLIDWORKS core functionalities. You'll need SOLIDWORKS installed at all times.
Can i just reference to the interop dlls that i can find in the api/redist folder of solid works or do they need to be registered anywhere?
Yes, you can. Actually that's all you need to do. These interops already have their types registered when SOLIDWORKS is installed. Your application by default will always use the latest version available of the API types in the production environment so be mindful what methods you have use.
I've tried to install the Solid Works API SDK, but absolutely nothing happend. No new folder unter C:/Program Files/ e.t.c
SDK should add a template to your VS templates. If that doesn't happen contact the API support. Meanwhile, you should take a look at the following resources:
SOLIDWORKS Forums API/Macros: How to write a SOLIDWORKS AddIn in C#? - YouTube
SOLIDWORKS API C# STANDALONE - YouTube
Component references and parent/child relations can you retrieve with 2016 SOLIDWORKS API Help - SOLIDWORKS Document Manager API Help
Document Manager API can be used without SW installed. SWDM needs license key, you have to obtain it first.