Change/Remove WordPress UI “Section Titles”

Sorry if the title is confusing. I wasn’t sure how to describe this briefly.

I’m working on a project for a small business and while I will probably be around to make changes as necessary, I also want other people to have access to the back end. I’ve found plug-ins and tutorials on how to change the wordpress logos on the login screen and other areas, but I’d like to make more extensive changes if possible (and without a plug in if possible).

I would like to change some of the titles along the left navigation. Specifically, we’re using all of the Posts section for the “What’s New Blog” and Pages for everything else. So, if I can I’d like to change “Posts” to “What’s New?”

In addition, I’d like to be able to remove some sections for some users. For example, we are probably not using comments for anything. So if I can remove the comments section that would be a plus. However, at the same time, it would be nice if the section wasn’t completely erased from WordPress so that the admin account can still see it and it could be used in the future.

Are any of these things possible with/without a plug-in?