Within your TweetEraser visible status interface you can select max. 3200 Tweets for deleting. Nevertheless on click the red delete button you'll be asked if you want to delete only the visible selected Tweets or maybe all Tweets found by your filter setting.
Thus, the answer is: You can delete as much Tweets as you want in one run.
Currently not. Only the Premium Eraser will keep your deleted Tweets as a kind of backup. The functionalities for restoring your Tweets are not implemented yet. I'm working on that.
But be aware, if you later decide to restore one or more Tweets you'll loose the time stamp of the original Tweet. That's because for Twitter your restored Tweets looks like new Tweets. They'll get the time stamp of restoring time.
Using the Twitter API almost each service is running into some limitations to the count of usable Tweets. Within this limitations all TweetEraser services are free to use.
For all other services TweetEraser is offering - e.g.
I'm asking for a small fee. For more information please have a look here