tweeting the same link?

how many different accounts can tweet the same link?
what happens if too many accounts tweet the same link? twitter accounts banned? link/site blacklisted?

same url can be shortened by goo.gl into different urls. would they be considered the same link?

As many as you want.

Nothing happens. I'm doing the same thing as well with url shortener on a bot and the accounts are still running now.

The danger isn't so much that they'll ban you for tweeting the same link (although they might; I don't know). It's that by tweeting the same link, you're creating a footprint. So if one of your accounts gets banned for whatever reason -- say, excessive following -- then they might all come down.