Brightline built Miami to West Palm Beach on rails it already owned, I think much of the new extension from West Palm Beach to Orlando has been on existing rails too.
Do trains require more staff per seat? Amtrak trains seem to have 2 staff in the car and I assume 2 engineers, and roughly (5 car consist of 72 seats) 360 passengers, vs 4-6 people for 180 people on an A320.