1 - Noise pickup on the leads is not what you need to worry about. If nothing else, you can put your detector in a shielded enclosure, with filtered power in and a hole just large enough for the IR to illuminate the array.
2 - What you do need to worry about is (as Kevin White commented) the effects of those long traces on the input capacitance of the op amp....
what changes to the circuit schematic does this imply,4
You'd connect the anode of the photodiode to a negative voltage instead of to ground.
what does "... providing a stronger field to sweep carriers out of the depletion ..." mean?
It means that with a stronger reverse bias, the field in the depletion region of the diode will be stronger, and ...
I'm not convinced you've destroyed them, especially if that is the 'after' photo. It's fairly hard to invisibly destroy most semiconductors.
The zero current probably was because you need to be on a uA range.
I assume you carefully flipped them to the correct polarity.
As to what is or was actually wrong (you may have introduced new issues), there is a very ...
In Step 3 you destroyed them,
by heating them to such a high temp so that plastic melted.
by connecting them in reverse due to which high current flowed and destroyed the Diode.
set your multimeter in microcurrent measurement mode and check current. it should be as shown below.
ref. Vishay Photodiode datasheet