For information about buying Dollar Coins from the Mint Start at this thread

Having lots of cards and missing payments is bad for your credit score. A quick search on this topic should produce relevant threads. There are general rules for credit scores, check out this post, but YMMV.
If you apply for too many cards you will start to get rejections.

Most Miles/Points Programs have some form of transfer, with either internal transfers to other members or externally to other programs.

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