Should on board jumper wires be solid or stranded considering integrity of the signal & noise?
For short distances (e.g. &lt; 0.1 m), stranded or not makes little difference for signals between ICs. I2C is not 100 MHz - max 2 MHz or so. In these cases, the greatest loss is from parasitic capacitance. 

Strands touching or not makes no practical difference -- signals between ICs have enough noise margin to make any difference imperceptible.