It's important to use the thick wires (12-14 gauge) to get the power across the longer distances. Once you've got it near the tracks, the smaller stuff (16-18 gauge) will work fine for the short runs to the tracks (2-5 feet).
Think of it like the blood vessels in the body. The big stuff is near the heart but as you move out to the extremities they get much smaller.
To connect the feeders to the track, the .110 spade connectors are good to use with FasTrack. Distribution panels or terminal blocks allow easy connecting between the heavier wire and something smaller.
The Wago connectors also give an alternative for bus wire to the feeders. These have lift up tabs that make them reusable. You just stick the wire in the holes, flip down the tabs and you're ready to go.
They can be found on eBay at reasonable prices. There are some copy-cat versions from China but I've heard that they are also expected to do the job.
