As many cameras as your TV can handle
How cameras connect depends on your TV's hardware: most TVs open them all together, and for older TVs one setting opens them in turn. Give each camera an RTSP address, H.264 or H.265, and an optional substream for the grid. HomeBoard plays as many live as your TV can decode, and shows the rest as their last picture.
When a camera fails, it tells you why, and keeps trying.