30 cameras is a lot more manageable if you end up using the customer's network connections. Just keep in mind it will be come a maintenance task to monitor the connection status of the cameras and reach out to home owners if a camera goes down for some period of time where you potentially will need to go on site to get the camera reconnected (if they change their WiFi SSID/password for example).
One way you could decrease the chance of having to make a site visit in the future is to put your own pre-configured router at each home where a camera will be mounted, and have the router physically connected to their own private router. You can then retain full control over these routers and the only time you would lose connection is if the home owners personal router bites the dust or loses connection to the ISP.
The above, combined with Axis one-click would be a fairly reliable setup and minimize the chances of having to run to someones house to reconfigure a customer network or camera.
With regard to streaming back out to the 100 home owners, multicast is not an option over the WAN unless the customer were to VPN in for example. And that would make the system more difficult to access (but more secure).
What I would do, if possible, is to limit users to using the web client and mobile client where you can implement resolution/framerate limits based on overall bandwidth utilization. I would also try to setup "zones" in the neighborhood and assigning cameras to different zones, and give the homeowners access to view video for only the zones they are authorized. I don't know about the HOA but if I was one of those home owners I wouldn't be very comfortable with neighbors from down the street being able to monitor my property which happens to be in the background of a camera mounted across the street from me.