You need to have a YouTube account linked to your Google+ account to comment and let others reply to that comment, so yes you need to have an account (be a member).
Yes, you must have a YouTube account, and subsequently a channel, to comment. As of 2016, accounts linked to a Google+ profile will not synchronize comments on YouTube to the other platform.
You need a youTube channel to post a comment. This is because YouTube needs to be able to display some name that is linked to your account.
YouTube comments used to be linked to Google+ posts. After late 2015, YouTube features are now being separated from Google+ so in the future, this should not be a problem.
It's easy. First, create your youtube account. Then, find the video that you want to comment on. Right click on the video and click on "Add a comment." Type in your comments, and then click on "Post comment."
On a video you just go to where it says "Post comment" under the video you want to comment on and for a YouTube channel, it's the same thing but some people disable their comments on their profile AND videos and that means you can't comment.
No, no one needs to pay money to comment on any YouTube video.
Yes. To comment on a YouTube video you must have an account, but there is no requirement to upload videos.
no. they can see a spammed comment just not a removed comment
The comment is posted immediately.
You need to register with youtube.com and open an account, then you can comment on videos.
You just need a username. Then you can automatically comment on videos.