Hallo Prahlad,

first: Your layout looks very nice now! You have seen, what the solid ground plane makes for you:

1. Providing a low resistive and low inductive ground reference for all involved devices of microcontroller circuit.

2. By this not only voltage drops resulting from ground return currents are minimal, but also between each two points on ground plane ground noise is heavily minimized. This results in an drastical decrease of common mode noise, means all devices which are connected to outer world are much less prone to radiate or to become susceptible against radiation!!

3. Ground plane extended over all signal traces in combination with guard trace arround certain points act as a shield, as if you have put the whole board into a metal enclosure. And this by only using a solid ground plane without making compromises!

4. Ground plane also provides a ground return current path for every signal trace next to it, and by this heaviliy minimizing created loop and as result, radiation from this signal trace and susceptibility against radiation.

So, you see how essential it is to use a PCB containing a solid ground plane!

There's a point, where you could even furtherly benefit from concept of solid ground plane, but which is not used up to now with your design:
A ground plane should also exist between certain digital signals on your top layer. And I think this issue was already mentioned by Russell. He is totally right, when recommending, that e.g. between the signals running to optos 6...9 a bit ground plane shoud be routed. This ground plane should also be connected to ground plane of bottom layer by several separated vias.
If you do this, then ground plane does also shield different signals against each other.
I think this is meant, when Russell recommended to sacrifice ground plane on top layer a bit: Share it in such a way (on top layer), that all signals profit from it, means if a certain portion of ground plane is also placed BETWEEN the signals.
The same is valid for the signals to input pins of SSRs: Sacrifice the solid ground plane on top layer a bit and place some gound plane also between the signals. There's enough place, and what's important, you still have this solid ground plane on bottom layer. So, you can sacrifice solidity of ground plane of top layer a bit.

I think Michael Neary stated, that supply voltage directly at SSRs, at R4...9 concretely spoken, should be decoupled by one or two decoupling capacitors. This, because the bridge (the yellow bridge in your layout) introduces some inductivity, degrading power supply decoupling at this point.

Could you connect the fixing wire of quartz like you did it with pin 1 of IC4, for instance? Fixing wire of quartz should be connected directly to ground plane, not via a separate copper trace.

Kai