There was a thread recently on singing heavy metel that desribes a lot of this perfectly so I won't go into detail.
I've done some playing around and find that I have different 'voices'. By moving my singing to different parts of my head, chest or throat, I can reproduce different singing styles.
As for stress on the vocal chords, lots of water really helps, as does proper warm up, and cool down. Build the ability of the chords over time to make them more resilient to long sessions. You'll find that there aren't many opera singers under 35 because it takes them that long to build the stamina and accuracy required to sing opera well. Building ability over time is the key to all night 'belt sessions' and being able to talk the next day.
There are a number of singers who have torn vocal chords - probably the most well known for this injury was Meatloaf. He was able to recover from that and return with a voice just as strong if not stronger than before. If you do damage your chords professional help is almost a must. Recovery can only happen by not overly stressing the chords during the recovery (basically slowly pushing them after a proper healing period) which a busy touring schedule doesn't permit. BTW, you'll find that some of the best concerts are the first ones on a tour because the vocal chords aren't beat to hell and back. At the end of a tour the range and ability of the vocalist is shot and the vocals often sound muddied or inaccurate because of this.
That is unless you're Ashlee Simpson of course....
(or any of the other singers that 'forgot' to sing on tour).
Can't help you on the guitar stuff. I do know somebody that could probably help but I haven't talked with him in a number of years and he's 5000 miles way. In the meantime I'm sure someone else will drop in with some recommendations. There are lots of talented artists that can assist with your questions.