Write tests section of Selenium/Node.js page links to MediaWiki repositories that already have Selenium tests.
WebdriverIO repository has example code. Please notice pageobjectfolder.
I agree that FAQ would be a good page to have. Feel free to create it and I will do my best to populate it with answers.
Please keep in mind that many questions are already documented upstream. Also, upstream has vibrant community. Any time I had a question, I got an answer quickly.