You can invite as many people as you need, up to about 20. Keep in mind that you may notice decreased performance and/or video quality with each additional guest.
Just copy the URL of your room, and send it. When they visit that address, you'll automatically see them appear.
You'll need a webcam and microphone. Headphones or earbuds are a good idea, too.
Yes — only those with whom you share the room's link can join your chat.
Wearing headphones or earbuds while video chatting usually solves this issue.
Make sure your webcam is plugged-in and turned on. If you are using the standard Vidless, click the wrench icon on your video box, and then select the correct video source.
If you are using Vidless HD, make sure you are using the latest version of Google Chrome or, soon, Mozilla Firefox. Also ensure that you have granted your browser access to your webcam and microphone.
And if none of the above work, try restarting your web browser.