Hi @shanetaylor13 I'll try to answer as best I can
On your first point. I believe a few vendors will offer discounts for students, military and veterans, I can not say for sure which ones as that's outside of my knowledge bubble I'm afraid.
On point 2, you mention you're with mint mobile, I assume (I may be wrong, it's just an assumption) that you're from the states, so I'll include a link to our forum for American users:
https://us.community.sony.com/s/?language=en_US
As they may be better versed in getting WiFi calling working on mint. As it is over this side of the pond, it's down to the network's currently on which devices they allow on the certain features like volte and voice over wi-fi, it's worth checking with mint if they allow the Xperia 5 to use it.
You can learn more at:
https://www.mintmobile.com/wifi-calling-text/
I hope this helps
