I'd like to address the question of the delay between energy production by fusion and light emission at the visible surface.
To start with, while the primary power source of every star is fusion, they also heat up by Virial contraction. This is important because it means that proto-stars are very hot before fusion ever sets in (and indeed the heat is needed to trigger the fusion). Accordingly the following description applies to all stars, even at the very beginning of their life.
The interior of a star is composed of very hot, very dense, ionized gas (that is a plasma). This stuff is very opaque, meaning that the mean range of a photon is short (on the order of centimeters). So it is appropriately in some averaged point-of-view, to say that a photon travels a distance proportional to its range, interacts and is re-emitted in a random direction. Wash, rinse, repeat.
You can calculate how long is required for the random walk to move the photon up to the relatively transparent outer layer and allow emission into space. It turns out to be a long time: many thousands of year for a star like the sun.