1. I don't think so
2. Author and curators get rewards as with Posts. A comment that has been upvoted/replied to cannot be deleted (but can be edited)
3. and 4. If you post via some applications, they have a benefactor reward. You can also set these for your own posts, but not using the Steemit interface. @dtube has a 25% benefactor reward for using their site, Steemit.com is 0%.
4. The nodes together form the Blockchain i believe, but am not 100% on this
5. https://steemit.com/steem/@jesta/building-a-high-availability-steemd-node-for-web-apis May help

If you found these answers helpful, you could vote for our witness - @steemcommunity

Cheers :)