Yes you can set your RSS Feed for post to "summary" on this page > Settings > reading and that will provide only the beginnings of your posts with a link to read the full post on the blog. But you cannot cherry pick out a paragraph to be used as an excerpt as the excerpt box on the Bueno theme is not active.
I’m sorry but the answer to your second question is “no”. Unless you use the P2 theme which is a Twitter-like theme the front pages of our blogs showcase content and comments are collapsed on that page and you cannot change this. The way the comments function is coded into the core of WordPress. By clicking the post title or the comments link the posts on the front page open on their own page where all comments display.
In a new blog one does not have many posts or comments. In an established blog if the comments did not collapse on the front page it would become a mile long in no time flat and page loading time is a page ranking factor. We have only seconds before visitors refuse to wait and click out.