How long is too long for interconnects?

Agreed LOL! 

Yogi is right, the distances the OP is asking about just aren't long enough either way to make much difference.  12 foot ICs are fine, balanced or un...unless he lives near a transmitting tower.  Ditto speaker wires, in almost any case that length won't cause adverse voltage drop or any other loss of signal quality.  Without any other details on the equipment in question, my advice is to do what works best for your situation and enjoy...

Since the OP has his system in his photo studio there might be more issues with noise caused by the lighting equipment. I don't know anything about photo gear but I'm guessing there will be dimmers and devices that control light flashes and what not with high current draws, which may contribute to more noise in a RCA cable. I have always followed the principle that RCA cables are fine for lengths of 10' or less and should never exceed 15'

I've never had an issue with long speaker cable runs. The longest cable run I had to make was 100'. I would bump up the gauge of the cable for lengths over 25' and I used cable that had a heavy rubber jacket.

My vote is for shorter IC's if using RCA connectors.