I experimented today with the iPad connectivity

It's possible to connect both the HDS and iPad to a mobile hotspot through my phone. The GoFree app was able to replicate the HDS display and the iPad still had internet. What I found, however, is the GoFree app would lose its ability to maintain a connection after a couple hours, then both the iPad and HDS had to be restarted. I bet this eventually gets fixed through software updates. When the HDS is connected to the hotspot, the GoFree was stable and maintained a connection for several hours without an issue. I'm going to have to come up with a way to get a charger to the iPad. There's no way the iPad can last all day with the display on all the time and turned up enough to be viewable outside in daylight.

I was able to take my kid's iPad minis and also connect them, so yes, more than one iPad can display and control the head unit. I think I'll stick to one iPad and will monitor the weather on or phones or maybe even get the XM/Sirrius module for the HDS.

I think this is a viable solution as long as you can be happy with the display size the iPad offers which is about the equivalent screen size as a HDS-9.