No it doesn't need to be prefired, I forget what purpose it is supposed to serve, not a necessary one though as long as you are competent in acquiring or scraping your RP.
No, those ratios are pie in the sky, you wish you could only use that amount and get away with it.
1g Ephedrine
2g Iodine
2g Red Phosphorous
That is if your really struggling with getting alot of precursors, and just use a few drops of water, or just use wet I2 instead of adding water at all. I know that is't accurately controlling the reaction, but if you want to bend the laws of science and chemistry that is how you do it.