I survey our recent work on assembling the modular function and dynamics of signaling casettes that regulate actin-based motility. Arp2/3-mediated branching of actin filaments is regulated by small GTPases of the Rho family. These are modulated by phosphoinositides. Together, such signalling agents determine "front vs rear" in a stimulated cell, where new actin filament ends are nucleated or uncapped inside the cell, and where protrusion or myosin contractility will occur. I describe how we explored such biochemical dynamics in both 1D and 2D cell motility models, and how we analysed their essential features in reduced mathematical caricatures. This work is joint with AFM Maree, AT Dawes, A Jilkine, Y Mori, and V Grieneisen. It is supported by NSERC, NSF, and MITACS.