Using a voltage drop calculator from the Internet, I plugged in 16 volts over copper wire at a distance of 8 feet and 5 amps. Using 18 AWG wire gives a voltage drop of 4%. 16 AWG yields a voltage drop of 2.5%. At 10 amps, these percentages are about double.
Since you want to isolate each power block, the feeders won't supply current to your moving train until it enters another block. If they were not isolated, then current from different feeders would share the load. And since electricity will take the shortest path to the moving train, the current through different feeders will be in a constant state of change.
What you could do with your control panel is use 2 18 gauge feeders to each of your isolated blocks. But one 14 gauge feeder would be better. Once you've covered the distance, you can size it down to 18 gauge again to connect to the track.
