Network or hotspot and using Volumio offline

I have two questions about the best way to set up Volumio. I’ve been using it at home and in my classroom (I’m a teacher) for maybe a year or so. I don’t have access to the network at school, so I brought in an old router from home and set up a network for just my phone, the volumio, and the occasional time I brought in my personal laptop.

With the hotspot working and the Pi3 having wifi built in, is there any reason to keep using the router? Either way, the Volumio doesn’t see the internet and only plays from the attached USB drive. The only thing I can think of is maybe better range. Are there other things to consider before I set things up for this year? Can I ssh in via the hotspot – just tried and yes I can.

Related to that and not exactly a Volumio question, but does anyone have suggestions about how to manage my phone connection? If it’s hooked up to the dead-end network, whether router or Pi based, it doesn’t seem to want to check the cellular network. Texts and emails come in sporadically at best. I assume it’s when I leave my room and go elsewhere in the building. Is there a way to automatically disconnect from the Volumio network, out in the real world, and go back to hotspot on a timer, like once an hour? Not a big deal, since it is my job, but it means my wife cannot reach me before or after school if I’m listening to music which can be a problem.

Thanks for any suggestions.