I'd be willing to bet a nickel right now that most of the people offering their insights and advice have NO EXPERIENCE whatsoever with actually undertaking such a project.
Sure, it SOUNDS like a fun project right now. How much of your personal wealth do you want to tie up in box after box of t-shirts stacked in your garage that racoons will use for bedding material? But wait! There's a BONUS! Racoons can carry parasites that will make you look forward to death!
So it's not ALL downhill!
OK, back to the nitty-gritty bottom line - or close to it:
Small, medium, large, extra-large, 2x-large, 3x-large (6 size groups)
men's, lady's and child's size categories (3 categories)
long-sleeves, short-sleeves, sleeveless, tank top, hoody, baseball style, etc (6 or more groups)
how many titles? Let's say four, just four starts.
how many colors? let's say four...
Multiply 6x3x6x4x4 = 1,728 shirts
This will give you ONE of each of the above shirt possibilities.
THIS is why you want to do a project like this using Cafe Press.
That's what I have done with my t-shirt and other designs.
If you go with Cafe Press, you still will sell almost NO shirts, but you won't lose YOUR shirt doing so, and the consequent bitterness will be almost palatable.
Go ahead, challenge me - dare me to reveal some of my experience in this field. i continue to maintain that the majority of your other advisors here have done NOTHING except form opinions about what you should do.