Interesting note about Teamspeak (I've only used it for gaming). My current batch of students (~18-20 year olds) seem to swear by Discord. The main reason being that it is more convenient to manage "servers" (If I understand correctly these are all hosted by Discord - but are "equivalent" logically to TS servers - access control, rooms etc). But they are easier to manage and shift between on the client side (I've only briefly looked at the chat app).
My personal intuition would be to try Mumble (as it's open source) - but if TS works, that's great.