I suggest reading Twitter’s own “Automation Rules and Best Practices” . I am currently building travel and tourism Twitter bots for every country on Earth . I’ve also got an inventory of non-travel Twitter bots I’ve made .
At this time, Twitter uses automation to “suspend” abusive Twitter bots. There is an appeal process, which works for me maybe 50% of the time. In particular, Twitter does not like “@” sign abuse; I’ve taken to replacing them with “#” tags (after removing existing “#” tags). Also, Twitter does not like people ripping off tweets without attribution of some kind (such as, at least a link to the original).
Since twitterfeed.com is rate limited, I now prefer dlvr.it. (BTW, Twitterfeed was acquired by bitly.com not long ago.) I have also used tweethopper.com in the past. Actually, feedburner.com now includes the native ability to pass feeds into Twitter. And of course, there are others.