Careful mixing metric stranding and awg , they are not directly compatible
Assuming droppers at 1-2 metres With a power bus close by
For droppers I'd suggest 16/02 , OD 1.6. , for the power bus I'd suggest 32/0.25 , OD 3.1m. , round about equivalent awg20 , and 14 respectively . This would be for a typical modern motors based locos.
Note that dcc does not typical have a live and neutral. Both rails are live at AC
Little can be gained by twisting the DCC cables. The operating frequency is around 200 kHz