DTF handles small type and full-color artwork better than a one-color screen, which is why the shirt configurator is built around a placement canvas.
The front print area is the chest. If you add the back, the price uses a 1.6× multiplier rather than a flat double — the setup is shared, the film is not.
Dark shirts need a white underbase. That is already in the shirt price. Very fine lines under 1 mm may fill in. The preview is a placement guide, not a microscope.