With regards to your Finder issue, unless I'm misunderstanding what you're after, you can click on the green maximise button (or, on OS X Yosemite, hold alt and

With regards to your Finder issue, unless I'm misunderstanding what you're after, you can click on the green maximise button (or, on OS X Yosemite, hold alt and click it) and the window will resize to fit the contents. Same goes for most apps (at least those designed properly for Mac), e.g. Safari, where it will resize to fit the website content. There is likely a keyboard shortcut for it as well but I'm not sure of it.