Where from this value comes? Are you sure you can’t use standard 82k value?
Why THT. When SMD began to be available for us we started to use them (about 1990). There is no problem to hand solder 0603.
I understand by the relay outputs. I’m used to have wide tracks connected to relay contacts. I double them - the same track at top and bottom (appropriate schematic to avoid crossing these tracks).
Seeing only PCBs I assume you have at the beginning the isolated DC/DC converter. Such converters frequently generate so high common noise that they need to be shorted (input to output) by appropriate capacitor to be in accordance with EMC rules. What datasheet says about it?
Many years ago we were asked if we can improve the device that its manufacturer had continuous problems with them. He had about 50 of them installed and got lot of calls to service them - disconnecting/connecting 12V supply wires helped. Their diagnose was: devices overheat and freeze. When I sow the PCB having 0 protection elements and with 1-wire touch-button socket connected directly to microprocessor pin I told them: The sequence is opposite - microcontroller gets latch-up (because of ESD from touch-button) and then consumes as much current as possible so regulator get hot and its thermal protection limits the current. So the regulator structure is kept at about 120°C and no wonder the housing of the device gets warm.
Your PCB is at that stage now - 0 protection elements. For each wire connected to device you should consider what kind of interference you can expect at it (ESD, Burst, Surge) and how to protect your circuits against them. It depends what is there connected, if that has separate supply and how long is the connection. Right software (ignoring for example short state changes made by ESD) is also a part of protection.
Remember that it happens that lightning strikes somewhere near the building with your devices.
Some time ago I posted here links to (in my opinion) very good papers about that:
See also few posts later in that thread other links I posted.