I got this offer last year also. Very generous! Of course, back then I still had the Mint to rely on for spending so it was pretty painless to complete. Given the cash payoff, you may want to consider using the bigcrumbs/Amex method to purchase $3K in Amex Gift cards each month to make sure you meet the required spend. I'd do a test purchase to make sure that Discover codes these as purchases.
Bigcrumbs pays 1.6% cashback for the cards, cashout through squareup at a cost of 2.75% leaves you with a net cost of 1.15%, or $34.50 for 3K spend per month, $138 for the total $12K spend. That leaves you with a straight-up profit of $362.
You'd be more certain to hit your spend target that way. I had a bit of a nailbiter last January as I didn't hit 3K for the month until the last day of the month!
Good luck and congrats on getting a great offer!
P.S.: If you haven't signed up for bigcrumbs yet, I'd appreciate the referral:
http://www.bigcrumbs.com/crumbs/land...dyandy&s=66804
Alternatively, there is a conga in the S.P.A.M. forum.