Depending on how many shirts you plan to sell and the profit you intend on generating from them, and if you plan to accept token currencies as well as fiat, have you looked into Bonfire? No money. Nice website. They handle the shipping and the emails. You just upload art and choose the options you want to offer. The more you sell, the more you make.

It's a very clean site and has worked well for me in the past.

Also, I heard that Amazon was doing something similar to this, as well...so that may be an option you may want to check out.

However, neither of these options support coins...so that's a massive downside. All depends on what you were wanting do with them.

Your art is awesome, @rubenalexander! Love seeing what you come up with. Cheers!