In reverse order, the page editor has some extra admin options around the text field, so this can affect the width. But remember, if your site is available to the public it will be viewed on different monitors at varying sizes and resolutions (and smartphones and tablets). It may be best to think of your layout as fluid, adjusting itself to fit many spaces.
Regarding your first request, I was not able to replicate that behavior. When I hit the Enter key, a new paragraph begins. It should be the same for you, but if you encountering a glitch then we would certainly hope to find out why. Which version of the BoldGrid Editor plugin are you using?