Tom,
The need for extra feeds to the track comes with experimentation and the observation of how your trains run. With new, clean track you may find that you can run your trains with only a single power connection at the center of the layout.
At the yard section, if you are using new switches with tight connections, the switches will pass the voltage to the tracks after them, and you may not need any extra connections. The same with the reversing loops.

In the end, assemble the track into your configuration, and start with one power connection and observe how your trains run. If they run satisfactorily, then no further connections may be needed. You may add more power connections if you wish, but it may not be necessary unless you see a marked decrease in performance at a certain point on the layout.

Larry