From memory, but it's been a while:
- Getting teams to join, sometimes on short notice
- Finding a Mumble server location that both teams won't hate due to ping and routing reasons
- Trusting teams not to use certain words that get you in trouble with Twitch
- Having someone host and babysit the mumble delay bots (also fix mumble flood protection settings so the bots can mass join)
- Dealing with desyncs during pauses. The delay bots are out of sync as soon as a pause starts until 90 seconds after the unpause.
- Getting casters to use the comms during interesting moments, breaking up their flow / desire to talk