FF9 is designed for 4:3 as far as I know. But I may be wrong. You might want to check Square's site to see if they mention widescreen support.
As for interlacing, I don't think there is a way to turn it off. But when playing in low res it's better to have interlacing.
Yes, small mistakes in soldering can be killer. At work once we had a board that would not pass the test system, and we couldn't figure out why. After 45 minutes of looking at it under 40x magnification we found a small crack in 1 trace on the board. Took me about 5 minutes to repair. It then worked fine. VERY frustrating.