I manage about 100 twitter accounts (for clients) and none of them have been suspended in the last year. A few get locked from time to time (which now you have to enter a phone number to get it unlocked, which is annoying) but no suspensions in the last year, so I'm very happy about that.
I use one proxy per 4 accounts (no matter how many followers they have). I think the reason my accounts are no longer being suspended is because I now follow and unfollow on different days. So on Mondays, Wednesdays, and Fridays, I do a bunch of following. And on tues, thurs, saturdays, I do unfollowing. Sundays I do nothing (Twitter might like this too).
I also have a strategy for how many to follow on each account, based on how many followers an account has. Keep in mind I have to be a bit more careful since I am managing client accounts, not a bunch of bots. I can't have a client's twitter account permanently suspended, and I need to have the balance between quality and quantity. My clients don't just want a high number of followers, they want targeted people, so they are happy with a steady moderate increase of good quality followers, instead of a super high number of random followers (or bot followers).
Here is my follow strategy:
Start off gradually the first month, no matter how many followers an account has.
1st week: follow 175 total for the week
2nd week: follow 245 total for the week
3rd week: follow 315 total for the week
4th week: follow 385 total for the week
Then starting the 5th week, I go by this rule:
For an account that has:
Under 2,000 followers: follow 750 per week
2,000-4,999 followers: follow 900 per week
5,000-9,999 followers: follow 1050 per week
10,000-14,999 followers: follow 1200 per week
15,000-19,999 followers: follow 1350 per week
20,000-24,999 followers: follow 1500 per week
25,000-29,999 followers: follow 1650 per week
and so on.
So, I follow the respective amounts on mon, wed, fri, and I unfollow the same amount, those who do not follow back after 4 days, on tues, thurs, sat. And for the clients who like to keep their following number low, I also unfollow the most inactive (even mutual followers) accounts about once a week, starting with 90 days since last tweet, and when that runs out, 60 days, and when that runs out, 30 days, and so on down and down. I try not to unfollow those who have tweeted in the last 2 weeks, but for those who want to keep a really low following number, I will unfollow up to those who have not tweeted in 9 days (the reason for this is because I account for people who might go on a vacation and not use Twitter during that time).
Settings for how often to follow when running: I follow every 4-20 seconds, and I unfollow every 2-15 seconds.
It's obviously possible to follow more per day than I do and maybe not get a suspension, but you have to figure out what's right for you and weigh the pros and cons of what happens when you follow more and more, with obviously higher and higher chances of suspension. If all your accounts are getting suspended at once though it's almost 100% because you are not using proxies, and you're not hiding your behavior well enough.
I use MyPrivateProxy. They have been really good and stable for the last year or so, and whenever there is a problem, just tell them which proxies aren't working and they'll replace them within 24 hours. I experimented with about 3 other proxy supplier companies before being satisfied with MyPrivateProxy.
This is the way I've been doing it without getting any suspensions in the last year. I feel very happy and proud of my set up now. This is also how I manage my own twitter accounts.
Good luck!