You shouldnt with todays computers. Back in the 5.0 days they had computers for specific parts of the US. Not sure if its still like that.
Ask Scott at Mile Hi. He would know from experience.
I wouldn't think you would. Your timing is going to stay the same regardless and if you keep an eye on your a/f ratio then you'll know for sure. Maybe it might mess with the a/f ratio but I'm not sure. Keep us posted whether it does or not.
You definitely want to check your A/F at the new elevation. This is another reason why buying a wideband more than pays for itself with the information it provides when you need it.