I am working on developing a 5 DOF robotic arm having 50 kg Payload using PLC, we are willing to source the integrated servo all in one (servo drives, encoder, and servo motor) with no breaks and external breaks have to be attached, and I have some doubts before sourcing servos that would this Integrated servo motor be convenient to be controlled with PLC accurately? IS there any chance of mispositioning or any inaccuracy in the case of these integrated servos? Is Controlling External break with the integrated servos reasonable?
Industrial servos with integrated driver and encoder have a limited power compared to non-integrated counterparts. Other then that, their spec sheet specifies their accuracy and if they are good/acceptable quality they will conform the spec sheet. You can extrapolate the positioning accuracy of your robot, based on your mechanism and the positioning (in)accuracy of each joint.
Depending on your country, sales representatives might be willing to work with you on finding the right motor for your application from their offering, but you have to break down the requirements to the motor level, you cannot go to them with robot requirements. It is not uncommon for industrial companies to admit, that they cannot fulfil your specs.
The Kuka iiwa 7DoF robot arm, the Schunk 6 DOF robot arm, the Pilz 6 Dof root arm are built with integrated servos. There is high quality precedent for integrated servos in robots, although payloads are lighter.
Depending on your targeted application(s), programming and motion synchronisation requirements and the chosen PLC, the PLC can be a serious limiting factor (!), although this was not part of your question, as I understand the question focuses on the integrated servos aspect. There is no precedent of a versatile industrial robot using only PLC (and servo drives, regardless of integration). If the task is highly specific, it might fit, but unlikely. It should be called a "positioning mechanism" (or similar?) not a robot, then...
External brakes are uncommon, but not unheard of. Depending on the (safety) certification of the robot cells your robot is placed in (e.g. CE, UL, ISO13849) "diy" brake integration can be a serious problem (not necessarily, highly application dependent).