I've used TweetAttacks Pro for building niche based accounts for about 14 months. In the past I would say that following/unfollowing 190-199 per day would be the way to go. I was doing that for about 38 accounts a day on schedule using 10 private proxies, unfollowing people after 3 days.
But then I lost multiple accounts and about 20,000 followers when Twitter started going crazy and banning back around early October. I initially had lost only one account and I shifted my strategy to much more random. I began not following/unfollowing every day. I lowered the minimum amount of people I would unfollow/follow to 100-150 and I began trying to tweet and retweet more tweets without links and popular tweets.
Even with those measures, I lost five more accounts. Since then, I've not followed/unfollowed at all. I don't use my accounts to direct message or wait and reply. I just tweet and retweet, so I'm not interested in churning through accounts. When my free time opens up soon, I'm thinking of making ten new accounts and starting them up and seeing what happens, while protecting my existing aged accounts.
I don't have all the answers because I'm still unsure why the six aged accounts got hit. They weren't on the same proxies and they weren't used for any heavy handed spamming. They had feeds from my blogs posting with a few of my own tweets/retweets a day.
In general though, I think you need to first make the account look very legit. Fill out the bio completely, add a profile picture and change the background to something custom. I would also think about feeding in some tweets from either your own content via plugin or rss feed. Make lists on the account, since that's something that no tool does that I'm aware of. Try to create some dialogue with your followers.
I would use Tweet Attacks very randomly. If you want to grow this single account for the long term, I would never follow/unfollow more than 200 a day. I would make the spread wide so that it doesn't look like an obvious pattern. With what happened earlier this fall to my accounts, I wouldn't schedule anything either. I would skip days to increase the randomness of it all.