1) The MixPad (more for FOH mixing) and OneMix (more for musician mixing their own monitors) both require iPads to work. Their is no iPhone/iPod or Android solution.
However there is also the CustomControl app. This app is available on all platforms (Android and iOS – phones and tablets)), but requires that someone create the initial layouts and control “surfaces” that the apps will load. Someone can create a layout to allow your musicians to mix their own monitors, but it doesn’t create itself. It takes some time and effort to get it designed and working correctly.
The MixPad and OneMix solutions are plug and play and require no custom setup to work, but are limited to just the iPad devices.
2) I cannot think of the max connections at this moment in time, but it is something like 32 devices if I remember correctly. It certainly is more than enough for the average use case IMHO.