No it doesn't include your username.
However, any usernames that you mention in your tweet are included in the 140 character limit.
There is no minimum number of characters that a Twitter username has to have. You can have a username with only one character, if you would like. There is a maximum number of characters that a username can have, though. A username cannot be longer than 15 characters.
Twitter posts are also known as "tweets" They are messages made up of 140 characters or less.
Each tweet can only be 140 characters.
You're allowed 140 characters with or without a link.
Assuming you mean characters, 140
A twoosh is a "perfect" update (or "tweet") on Twitter. Specifically, a twoosh is a tweet which uses every character of Twitter's 140-character limit, being exactly 140 characters in length.
There IS a limit to tweeting. If you tweet more than 1000 tweets per day, you go to twitter jail for a day (basically means that you can't tweet anymore). If you tweet more than 100 per hour, you go to twitter jail for an hour. You also can't write more than 250 DMs per day.
Yes you can. Arguing on Twitter is actually very common. You have to summarise your argument up in less than 140 characters though.
Not unless you want to post pictures to your page. Twitter is a site to post updates on in 140 characters. No pictures necessary.
Yes it includes punctuation.
Yes it includes URLs.
No, Twitter's 140-character limit does not include punctuation. Punctuation marks such as periods, commas, and exclamation points are not counted as characters in a tweet.