Very belatedly getting back to the Betazed aspect of things, particularly the Federation-Betazed history aspect, for a moment...
Okay, first contact between the Federation and Betazed happening within a decade prior to Tarsus IV, not an issue. The Betazoids' alleged attempt to keep their telepathic abilities to themselves seems doomed on its face, especially depending on how long the Federation/Starfleet people had been keeping watch on that system, and how much access to Betazoid civil communications was possible, how much content from that access was archived by the surveillance/scouting teams, prior to official contact.