Not really but this would be better handled by a custom BBCode anyway. Just create a custom BBCode for a generic video tag.
I've looked into Amazon but I haven't been able to find an official documentation about creating product links (which I believe is what the iframe thing is, what they call a "product link") that does not require an associate account.
Yes, specific tweets only. If you meant you can not find the URL, you can get it by right-clicking the date of the tweet.
I don't think it can be used to display the latest tweets of an account, but it might be a feature I'm not aware of.