The Stewart parallel mechanism is used in various applications due to its high load-carrying capacity, accuracy and stiffness, such as flight simulation, spaceship aligning, radar and satellite antenna orientation, rehabilitation applications, parallel machine tools. The dissemination of such parallel robots is however limited by three factors: the limited workspace, the singularity configurations existing inside the workspace, and the high cost. In this work, a simulation environment to support the design of a cost-effective Stewart Platform-based mechanisms for specific applications and to facilitate the choice of suitable components, e.g., linear actuators, plate sizes, is presented. The optimal design here presented has multiple objectives. It intends to maximize the payload and minimize the forces at each leg needed to counteract external forces applied to the mobile platform during positioning or manufacturing applications. These objectives can be achieved through a dynamic optimization. It also aims at avoiding reduction of the robot workspace through a kinematic optimization.