Stress
As someone who earns their money by writing poems from their couch, you should still expect some stressful moments. First, even though they're called "greeting cards" doesn't mean they're all just elaborate "Hello's." Many of them are about death, loss of loved ones, illness, separation, break-ups, and saying goodbye. To write them, you'll need to tap into similar moments in your own life. Keep the tissues and therapeutic tub of Baskin-Robbins handy.
Second, have you seen the greeting card market? No walk in the park. Money matters will get stressful, especially when the owner of a local shop lowballs you on the greeting cards you're supplying, while the local florist, also a longtime customer of yours, says she's "no longer interested."
And by the way, if you're looking to minimize stress in this job, avoid checking your bank account. That number ain't gonna be pretty.