Yes, they are pronounced differently. 1st "close" is pronounced with a 'z' sound, like "cloze". 2nd "close" is pronounced with a 's' sound.

Yes they do have different sounds. to close down - this is pronounced with a z sound like 'cloze', emphatic z sound at end. close friend - no z sound and clipped and short in speech. Hard to write but something like "kl ' os"

Yes. I suggest the following site which has a person say aloud the words or sentence that you have typed in. Choose the accent that you like after you type in your word/sentence. http://www.oddcast.com/home/demos/tts/tts_example.php?sitepal

They have the same pronunciations, but different meanings for example the first close meant to be shut down or shut the door but the second means his/her best friend ( a friend that she/he knows her really good).

Yes. "Close" as a verb (to close) has a "z" sound. As an adjective, it has an "s" sound. Basically, we need to hear that the verb is a verb. A few other words follow this rule.