Question
Does AMEX enforce their fine print by only allowing bonus miles on the first Delta Skymiles account opened?
Answer
Yes they do. However, if you an the card with a 10k bonus and the tried again when they increased the bonus to 17.5k you'd get the difference of 7.5k.
Answer
Bonuses for personal and small business cards are counted separately, so you can get both. If you don't have a true small business and an EIN, you can declare sole proprietorship and use your SSN in place of an EIN.
Answer
You can also get the Delta Amex Gold - get the points - and then upgrade to the Plat. for another points bonus (I think I got 5,000 more).