Print on demand is a bit tricky, especially if you use photos on your products. Some of the POD sites are really picky about trademarks that may happen to have gotten caught by one's camera in the midst of a larger photo. Then all your products using that image disappear. Sometimes places you'd never suspect have trademarked names. Some owners appreciate the publicity and others complain and your products are taken down. Some people put slogans on shirts, etc they don't know are copyrighted. I just had five best-selling postcards get taken down on Zazzle after being there for several years with no complaint. So you never know.
I am interested in learning more about Bitcoin since PayPal started accepting it, but it still doesn't make sense to me. I'd also be interested in reading recommendations from people who aren't marketing it.