I've seen plenty of security personnel and access to the platforms is only with a ticket.
Access to the platform only opens up when the train arrives. Until then you wait upstairs in a Lobby like area.
So far from what I've seen their hasn't been an issue with the homeless. I see the homeless walking up and down Broward Blvd, stand outside McDonald's and stand outside KFC but NOT at the Brightline Station.
Thanks! Your answer is awaiting moderation.