Hallo Prahlad,

your layout becomes better and better!

Some points should be changed, though:

1. Remove the ground plane and signal lines under the opto couplers (by the way, 'Optokoppler' would be the german word for 'opto coupler'...). All signals connected to the input side of opto coupler should be sparated to all output signals (also ground plane) by the distance defined by the according solder pads of opto coupler, namely more than about 5mm. 8mm would be optimal. That's the distance the well known safety standards demand if one involved signal can carry a dangerous voltage, by the way.

2. What I said right now, is especially valid for the signals arround the SSRs. If output side of SSRs can carry dangerous voltages, then you need to maintain a safety distance to microcontroller circuitry of at least 8mm. This is valid, if you use saftey class II power supply for your microcontroller board and if output side of SSRs is connected to mains voltage.

3. Opto couplers are always prone to become damaged by voltage spike exceeding rated isolation voltage. As the coupling capacitance between input and output is very small, which is needed, of course, to limit interference coupled from one side to the other via charge injection, even little portions of charge, how they are observed with ESD events, can develop a destroying overvoltage.
Do always handle the opto coupler terminals, which are fed via your SUB-D connectors to outer world, as if they very very sensible points! Choose 'female' connector for your Sub-D connectors, so that pins cannot be directly touched.
Another way to prevent the develop of destroying overvoltages at the isolation barrier, is to use the following scheme:

Let your PCB be device 'A' and let the equipement where you connect opto coupler signals to, be device 'B'. Connect both devices by shielded cables. Connect shields at the side of device 'B' to signal ground of device 'B'. I mean the ground, where the driver and reciever circuitry of otpo signals is connected to. Now cable shields carry signal ground of device 'B'.
On the other side of cables, namely at device 'A', connect the cable shield to chassis frame of SUB-D connectors. Connect all these SUB-D chassis frames together and connect them to signal ground of device 'A' via a varistor showing a threshold voltage of 500V, or so. Parallel the varistor by a resistor of 1MOhm.

This scheme works as follows:
If you connect device 'A' and 'B' by the help of this shielded cables, then any dangerous charge sitting on ground 'A' or 'B', perhaps from a former ESD event, will flow over the shield and via varistor from ground 'A' to ground 'B' (or vice versa). As consequence the stray capacitance of varistor will be charged up to the moment, where the threshold voltage (500V) is reached. Then, varistor becomes rather low ohmic and charge flows directly.
The effect of this protection scheme is, that any overstressing of isolation barrier of involved optocouplers is prevented. After the dangerous charge has flown, varistor is discharged to zero volts by the 1MOhm resistor.

This scheme must only be used, if both grounds ('A' and 'B') do not carry any dangerous potential, means if circuitry complies with safety class I or II standard!!

4. Switching SSRs can produce some interference. Also, via cables to outer world interference is fed very near to your microcntroller circuit. This can make troubles! To prevent trouble, you should keep microcontroller circuitry and output side of SSRs much much farer away from each other.
Sometimes, it can be helpful even to add a metal plate placed close over the micro board and connected to ground plane at several places. This metal plate will act as a shield: Every stray capacitance to the SSRs and their loads will end on this metal plate, and not inside your micro circuitry.

5. If SSRs are connected to mains voltage, take care that safety standards are fullfilled! Means, screw terminals are only allowed, if mechanical stress on the cables will not hit the screw terminals. Also, take care that necessary safety distances are guaranteed: Use of double or enbhanced isolation and providing safety disatances of at least 8mm!!!

6. Russell mentioned, that erroneously reverse connecting +5V power supply will result in a lot of smoke. Well, if a standard +5V regulator like LM7805 is used, the built-in SOAR protection would hardly allow to flow a current which is suited to damage a transzorb! If an LM7805 is short-circuited, then a rather high short circuit current of about 2A is flowing. This results in a tremendous heating of die, which in turn activates SOAR protection. As result, this high short circuit current would only flow for short period of time.
This is a nice example, why power supplies should never be heavily overdimensioned. With suited power supply, there's enough time to notice the misconnection and clear the situation without fabricating of smoke...

Kai