For the 1st question it's all about de tuning and recording right. So, get close the mic, use a pop filter and say what ever in a deeper voice. Detune, eq, de ess, compress (compress hard), vocoder to taste and wide af with ozone imager. You can go further via a frequency shifter or little alter boy. Reverb at the end.
For the second question learn how to reharmonize and make your song on a piano first. Even if it's hardcore techno, get it to sit right and work from there. If that is not your thing go to soundbetter :).