The number beside Auto Retweet in the membership plan refers to how many retweet settings you can create.
For example, if you want to retweet every time someone uses the hashtag "#hopscotch", it would count as 1.
This number is also per account, so if you add 2 twitter accounts, you can set up 10 retweet settings for each twitter account if 10 is the limit for your plan.