When an ABR client is connected, the client will consume a single stream, at a single rate. They will not be streaming all or some of the bit rates, simultaneously.
Some other comments, related, that you've likely already considered...
Upload Speed: If your viewers are connecting directly to your server, in your house, then your Internet upload bandwidth capacity will determine how many clients can connect. A key factor that can help you control how much of your bandwidth is used is the bit rate setting for the streams you are serving. This can be set when the video is encoded to a file or when published to Wowza as a live stream (you will see a bit rate setting in all encoder applications).
For example, let's say you have a cable broadband Internet service that runs at 25 mbp/s down and 4 mbp/s up. We would use the 4 mbp/s as the constraint. Let's also assume your stream is running at 350 mbp/s for audio and video (don't forget to combine the audio and video bit rates). Finally, let's maintain the best practice of leaving 20% of the bandwidth available for "overhead" which gives us about 3200 kbp/s (3.2 mbp/s) to work with. If we dived 3200 by 350, we get 9.14, which should be rounded down to 9 - this is the maximum number of viewers that you can serve on this connection at 350 kbp/s.
In other words, use this formula as a guide:
(stream bitrate * max concurrent clients) < server bandwidth
Transcoder: Wowza offers a live Transcoder AddOn that can produce multiple bit rates for a single stream. That means you can send a live stream to Wowza at 750 kbp/s which would be transcoded into, for example, an additional 550 kbp/s, 350 kbp/s and 150 kbp/s stream, real time. Using adaptive bit rate streaming (ABR), you can instruct the players, on the client side, to select the best available stream/speed. This means a single viewer will enjoy the 750 kbp/s stream, when conditions are good, but as the number of viewers increase, the players will switch down to lower bit rates, allowing you to host more peak users, at lower bit rates.
VOD: ABR streaming also works for Video On Demand, which doesn't use the transcoder, but uses media files that are encoded especially for ABR delivery.