Hi M, welcome to KM
The first question is easy, middle-clicking to open links in background:
The second, opening all bookmarks in a folder, works differently then you seem used to:
First edit bookmarks and give that folder a nickname of your choice.
Then later, when you type that nick into the URL bar, just hit enter.
The FAQ you find by menu Help>FAQ
The second link was Help > K-Meleon Wiki > Tips and Tricks