I dont believe so , probably against Adsense TOS... https://www.google.com/adsense/static/en_US/LocalizedTerms.html?hl=en_US
Yes, they did. However, make sure both of the ads don't look the same (so don't use the same ad colors)
I think its OK to do that now. A lot of people are trying Konetera recently a s a rsult of Joel Comm's thread.
That is incorrect. You are allowed to have both now. Even Joel Comm started a thread on DP about this (use the search button)
Yes, you can use it and I started last month using both adsense and kontera on same pages and I am waiting for my first payment in kontera of $125