Hi Michel, let me answer your questions:

1) Google+ is important to share your posts and make your website noticeable to the whole world. Social Media is one of the best means of traffic nowadays, so if you should be using FB, G+, Twitter, Pinterest, etc etc

2) Comments count as content for that particular post/page. So if you write a blog post of 1,500 words and you have comments for 5,000 words, your post will be 6,500 words in total. that's how it works.
If someone comments on your blog post is because he read it and he has a question or comment on that particular content. Unless you are buying comments elsewhere (which I don't recommend).
If you ask for comments here at WA and you don't feel comfortable with what they posted, you can simply reject the comment and they will replace it for a new one.

Hope it helps :)

Hi sorry Im new here. I dont know the answers. Im following you. All the best regards. I think google is important to your website to get it ranked by google because it is one of the major search engines.