When I built a small 8x4 layout for by grandchildren, I used 16 gauge wire. For my own layout, where I run multiple locos, 14-gauge stranded.
"Buss wiring" can mean different things to different people. I have a common buss (bare looped) all around the layout, into which everything is connected. My 6 TIU outputs feed areas of a control panel, on which are toggle switches from which 14-gauge wires run to each of my 70+ blocks. Some runs are over 30' long. Blocks are quire short, as layout was designed in the last century to run conventional locos (that's all we had).
No signal problems.