If a famous person has a Twitter account, you can tweet them as often as you like. However, I would suggest not overdoing it because you don't want to appear to obsessed and scare them. But if you want to tweet them once or twice a day, then I say you should go for it!
There is no problem with reply to an old tweet by someone famous.
You receive a tweet when someone mentions you in their tweet.
To do a retweet on Twitter by someone famous you can either use Twitter's in-built retweet function or type 'RT@username' where username is the famous person's username on Twitter and press 'tweet'.
When you send someone a tweet using Twitlonger your tweet will end with a link that someone can click on to read the rest of your tweet. They can't access anything in your account they will only be able to view the tweet.
You can send a tweet to someone by beginning your tweet with their username (@username)
Simply start your tweet with the '@' symbol and their username.
Yes, simply put the '@' and then their username in your tweet.
If you mention someone in a tweet, it can still be seen by everyone. Only direct messages are private.
Yes. As long as you don't start the tweet with the persons username and mention them in the body of the tweet.
If they like what you tweet about.
If someone that DOES follow you retweets you and someone sees that tweet on their TL they will RT you.. and they don't have to be following you... Follow me @ALexisU_
If your tweets are protected then the "retweet" button is not available on your tweets. However, this doesn't stop someone who is following you from copy and pasting your tweet to a new tweet and adding "RT" before it.