Hey & welcome to GT!

Originally Posted by: dio1ne

is there a nice overview for the most important 7th opan chrods, like A7, D7, C7, G7 and so on too?

I'm not aware of any single chart with all of them. I will look into that! For now, the toolbox has a chord chord that you can use to find them.

https://www.guitartricks.com/chords

And I have a tutorial on all the basic dominant 7th chords.

https://www.guitartricks.com/tutorial.php?input=479

Hope that helps!