How many Twitter followers should I ideally have on my Twitter accounts before I start posting promotions (contests), coupons, deals and/or selling items to my Twitters followers?
I think it's more about how much interaction and information you have already tweeted, not how many followers. You could have 500 followers and if you start slamming them with promotions, they'll unfollow or just ignore your account. Tweet useful information and sprinkle in your promotions. Best of luck!
Based on stats from our subscribers they have on average 2000 followers and follow around 1600. But for regular users it is around 400. http://www.vicconsult.com/twitter-followers-following-ratio/
It's not the number of followers that matter, it's how active and engaged your followers are. You want to look at this from a quality/quantity standpoint. When are you starting to get good interactions & engagement from your followers through your normal day-to-day tweeting, that's a good sign it's time to try and harness the buzz you've created and expand to a new group of followers with a promotion. Remember, it takes time and hard work to create anything good.
The fact that they have followed you is just the start. You have to keep getting on their radar so that they notice you when you tweet. Otherwise they will just ignore you and won't click on your links, even though they are following you. The way to make that impact is to consistently tweet good relevant info. Also, engage with other users by retweeting them often and replying to their tweets every time you log in.