1. The black boxes are called Coil Packs.
2. Why would you wanna double up and increase gapping?
3. Your theory seems a bit off... Creating more spark will have an effect but not something that drastic. Sounds more like a fire hazard then anything. Ever thought about just replacing, or possibly going with a larger the stock wire size. Magnecor makes a 8.5mm wire set if your interested in better sparking.
4. Toyota probably designed the spark system a certain way for a reason... Unless you know you shit very well.. I wouldn't suggest doubling or changing gap size. Especially for increased power purposes