Instructions for how to run more than four motors from a single Control or Expansion Hub using a REV Spark Mini. Westside Robotics have a number of other tutorials available as GitHub repository wikis.
A presentation from "Quantum Stingers", team 13380, that discusses different ways to build mechanisms the expand linearly, both horizontally and vertically.
A presentation from "The Antidote", team 14320, that outlines the different ways that gears, sprockets, chains, belts, and more can be used to transfer motion across a robot.