Hi Jakob and Sebastian and welcome to both of you to the forum,
Let me start by saying that we're sorry that you feel that the forum here isn't much help at at all. As the forum manager, I'm personally very proud and protective of the effort that goes into running our forum and the assistance we provide to members through it, so I would of course completely disagree with your assessment.
Now, in regards to your questions.
1. My suggestion is to use phone contact as the best means of dealing with a supplier. Of course that may not always be possible, so email is the next best option.
2. All you have to do is say that you are inquiring about establishing a Dropshipping account with them and inquire as to their terms of trade. Some my well have all that information already displayed on a website, so certainly best to see what you can find out about them before contacting them.
3. Suppliers will give you complete access to sell all their products once you have an account with them. Just be aware that some suppliers will require an account fee for new account owners, other charge a monthly membership and some are completely free, so you really have to work out what the best option for you is.