Good for a start.
Some improvements I could suggest portraying a customer are mentioned below :
1) Would like to have more varieties, and You need to be more creative if you're targeting t-shirt meme market.
2) My opinion : I did not like the background white of the Website, work on it.
3) Add filters too
Hello Lazy Boomer, you have started your own website and the work of shirts printing. As colour printing is a good thing to do so, especially if you have a creative side then it is best that you go for the one you like the most. As the designs are based on memes so I guess that they will get a lot of fame as people of all ages like memes and would love to have their favorite one on their chosen shirt. With time there must come some diversity so there is the possibility that your work will evolve, but for a starter, it is a good one that you just showed to us. The only downside I felt is the website color scheme. It is a bit dull but according to your idea of memes, it should be colorful and attractive, so maybe try some darker sahdes.
I checked the resource shared by you but I think you must rethink the designs or you can get some help from the other sources like MasterBundles where you have many options of graphically designed t shirts. I am also using this website and I am happy with their work.
Any meme is relevant for no more than one month, so you must constantly monitor trends and adapt to the new trend if necessary. Sometimes memes appear completely by accident. I've always liked memes because most adult clothes are made in dark colors. Even though I'm an adult, I want to feel like a kid sometimes. That's why I recently bought a few things from unspeakable merchandise. I love to play Minecraft, and this YouTuber is one of my favorites.