Show me the money!

Biggest issue I see people having with what you're thinking of doing is in the marketing of the end product. Having great designs is (my opinion) probably the easy part. The next easiest part is finding someone to do the printing. The tough part is figuring how to get noticed by the public.

Retail t-shirts (again, my opinion) tend to be impulse items - someone sees the shirt, likes it and buys it. Online t-shirts tend to be "focus" driven ..... people are looking for a specific subject area, sees the shirt, likes it and buys it.

Trying to develop a "brand" with unique shirts is always going to be tough.

Remember there is a reason why the "big" online retailers of designed t-shirts will have literally 100's upon 100's of shirts on display on their site (a potentially massive investment).

I am "strictly" digital print and focus on a low-volume niche (those needing under 24 shirts). I do have an Etsy site but hat produces well under 5% of the total business. 95+% comes the old fashioned way .... people referring other people for small businesses, church groups, school groups, etc. And that 95+% is taking their design and simply printing it.

@paradigmprint said it very well!

If you need something that is going to provide for you and your family, do not look to your own line/brand. But if you enjoy doing it, and have some time and money to spare, then not much harm in giving it a try and seeing how far you can take it ... but don't expect it to replace the Day Job any time soon, or probably ever.

Marketing (I believe) is the limiting factor for small creatives. Snorg or Busted Tees can afford to advertise and win the search results battle because they have 1000s of designs, so once someone gets to their site, there is so much more for them to see and potentially buy than in my case, where I have about 80 active designs. Also, "Best Dad Ever" and "Fart Loading" sell because they are well-known memes that appeal across a broad spectrum. Your original art/design will have a very tough time getting found in search results if no one knows it exists, and thus can't search for it. It helps to have at least some designs that relate to current events, popular culture, or mundane blather like "Best Dad Ever." All while staying well away from, and out of trouble with, images and names owned by others: sports teams, movies, musicians, etc.

For the record, I sell my own line of designs which I print myself. I have no one to support (unless those damn little ants count), and my burn rate is very low. For me, T-shirts are intended to be one spindly leg on a multi-legged stool.