The "BEST" plug will depend upon many factors. Plugs come in different heat ranges to meet the needs of engines with different compression, timing and nitro. There are other variations on plugs such as idle bars.

A blanket statement like OS#8 is the best plug is not very informative nor is it correct. An OS#8 works well in most sport two stroke engines on moderate nitro. For high nitro/piped or four stroke applications, an OS#8 is a terrible plug.

My guess is that there are many plugs that will work well in your K&B engine. Any general sport two stroke plug will work fine.

Ditto on the 12V. 12V will fry your plug quicker than you can disconnect the battery. You need some way to reduce the voltage to about 1.5 volts. A power panel will work.

Cheers