Hi Russell Thanks for your post.

if you can have a fairly good groundplane on a 2 layer board you'll save a lot of money and be able to combine both parts onto one board

I will have to think again on the 4 layer issue.

the interconnecting wires make good antennas

True, But in my case the interconnecting cables carry signals of very low frequency as the interconencting cable carries outputs for Triacs switching and inputs from Proximity switches.

having two boards doesn't necessarily mean you'll be free of EMI and coupling issues

I am spliting the design onto two boards just to save the cost no other intention.

Regards & Thanks,
Prahlad Purohit