We present a novel E-textiles toolkit that can be used in the rapid prototyping of electronic textiles during the research and evaluation phase. The modular, Arduino-compatible toolkit incorporates various sensors and control and communication modules. The needs of fashion professionals have been considered during the conception of the toolkit, which was developed in close cooperation with partners from textile research institutes, the textile industry, art schools and design. After the initial manual prototyping, the toolkit modules can be directly transferred to reliable industrial integration using advanced machinery. To achieve this, we developed the E-textile Bonder, a machine capable of mechanically and electrically connecting modules to textiles with integrated conductors. This paper gives an overview of the toolkit as well as the design considerations discussed and implemented during the cooperation with textile industry stakeholders. Furthermore, the integration process with the E-Textile Bonder is described, and its advantages over other technologies are discussed.