I am new to the miles and points game, and have been reading a lot of posts here and on blogs to try to develop a strategy. I have developed a few questions along the way for which I can't find definitive answers. I can only meet 3-4k minimum spend every 90 days, so I am trying to maximize it.

One thing I am curious about is how to churn cards from each issuer. The main ones being Amex, Barclays, Chase, and Citi. I have seen bits and pieces about their policies, but they seem to be very different and I have not gotten a real idea of how to approach doing this with each one. Here is my impression so far, correct me if I'm wrong and I am interested in your insights.

Barclays: Can apply for 1 card every 6 months
Chase: Can apply much more frequently , but have to wait 18 months before applying for the same card again to get bonus
Citi: I'm not sure but it seems like they are fairly strict
Amex: Can have 3 or 4 cards at once, but often have to wait 12 months before applying for same card

Also, does anyone know a foolproof way to make sure I actually get the bonus? I read a post on here from someone who had been told by American Express they would get a bonus and were later told they're not eligible.

Basically I could use any advice you can give, even if it's not directly answering these questions. Thanks!