Definitely read up on the threads here to keep up to date and you will also see members mention what the offers were like in the past. Even though the points/miles are what we are after, I wouldn't focus too much on it and hesitate on jumping on a card if you have a need for it. The offers will probably be ever changing (up or down) so there is no way to tell for sure.

What do you want to do with these points/miles? Any specific hotel or airline in mind? There's the Club Carlson card by US Bank and Priority Club card by Chase. You mentioned Delta, but will you be flying with them from your hometown or is it better to get another card like the Citi AA, Chase United, Chase Southwest cards? You have a lot of options available. Regarding the business card, they are usually considered a different card by itself so you should be fine applying for it on the same browser. You might need to call in to explain the reason for the second card.

Depending on your credit history (credit age, credit limit, any late payments, etc.) with those 3 cards (are those your only credit cards?), I suggest applying for one or two cards for now.