The CSR travel credit is usable each card member year. The annual fee is $550. So, if you use the $300 credit during the first year, and then use it again during the first 30 days of your second year, when you cancel the card the 2nd annual fee will be reimbursed and you will be +$50. If you don't have travel plans, you can always book a refundable Southwest flight, then cancel the flight once the credit posts and you can use the refunded money for something else. You don't have to cancel the CSR either, you can downgrade it to a Freedom or Freedom Unlimited and enjoy those $0 AF cards and still get the CSR annual fee refund.
Business credit cards are offered to businesses. The application will have a section for the business applying and the underlying officer or owner that looks very similar to a personal credit card application. Individuals, even those without real businesses, can apply for business credit cards using their SSN as the Tax ID number and applying as a sole proprietorship (your title would be "Owner"). If you were ever asked what your business is, you could say you sell things on
Amazon. Personally, I say my business is "[my real job] consultant". For business income, list at least $1,000 (I use 10% of my actual income). For time in business list 1 year -- this way you can say it is a new business and your business income is your anticipated income (e.g. no business tax returns filed). I have never been asked any of these questions by Amex or Chase -- and only once was I asked to confirm my business mailing address (same as my home address).
You can also register with the IRS to receive an EIN for your sole proprietorship (again the name of your business is your real name). Chase treats EIN sole props as different than SSN sole props so you can get more of the same business cards (e.g. 2 United Business cards for 300k miles). It's a means of expanding your number of SUBs.
For someone with as lengthy a history with Chase as you, a MDD won't be that risky. But, you would have to meet $8000 in MSR in 3 months, so you may have to spend a little beyond your budget on actual purchases or look into manufactured spending options like sending your spouse money on Venmo (and paying the 3% fee).