This paper focuses on optimizing the kinematic structure of a robotic manipulator for a given task. It is a planar manipulator with three degrees of freedom. The problem of designing the kinematic structure of the robotic manipulator, which is assumed to have a modular structure, is addressed. The aim is to find the optimal combination of the lengths of the individual segments that will allow the execution of the specified task. A Genetic Algorithm is used to find the optimal combination of lengths. Planning for collision-free paths is also part of the solution. The path must ensure that the manipulator completes the required task without collisions. The Rapidly exploring Random Tree (RRT) algorithm is used for path planning. Based on this path, the motion trajectory of each link of the manipulator is then designed and optimized. A hybrid optimization approach is used for trajectory planning, considering both time and jerk. The overall approach is directly linked to the concept of modular robots, where flexibility in the composition and adaptation of the kinematic structure play a crucial role in solving diverse tasks in robotics. This work presents a methodology for addressing these challenges through a systematic optimization approach.