To get your API key you can log into your account here:
http://www.envolve.com/admin/
"My Sites" is a tab in the upper right hand corner after you log in. If you haven't already registered your site you will need to do so in order to get an API key. You can do that here:
http://www.envolve.com/sign-up-and-price
We know branding is important to any serious site. We call our unbranded versions "White Label". If you get any Premium or larger package there will be no indication that you are using a hosted service. Your users won't know the difference, and they won't see our brand.
You actually can move the windows around. You can pop them out into a separate window and then put them wherever you like. Just click the little arrow button in the upper right corner of the chat box.
In regards to the reduced feature set as compared to some other chat services... we do have skinning options and analytics available with paid accounts. We don't currently do emoticons or colored text, however. We've been trying to keep everything super-simple. We figured people who wanted the those features would just use the forum threads. Are these features important to you? Which ones are the most important?
I really suggest you just give it a try and see what you think. Install is super simple, and the system will make a whole lot more sense after you've played with it for a bit.
Hope that helps! Cheers.