I am working on my 10th one. This one is more of a challenge as there is no way to get all blocks the same size. I would suggest poly batting to help with the weight. They can get heavy. I like to quilt around the designs on the shirts rather than an overall meander. First I always measure the designs and see what size blocks I can get and then use Graph paper to design it and layout the shirts. I also will change the thread colors to match each shirt which can be a pain but looks nicer. I use poly thread because I have the most colors. I keep a piece of the wonder under paper backing and use that to press over the designs and prevent sticking. Sometimes you have to quilt into the tshirt paint especially if it is a big designs ... Make sure you use a new needle so it is sharp and can penetrate the paint easily. I have also done some cut and paste i.e. Take the numbers off the back of sports shirts and using wonder under stick them onto the front and applique them then quit around them. That takes up some of the blank space if you have a small design on the front but need to use a large block to maintain a size.also I recommend using cotton dashing in lieu of sewing them block to block. That helps break up the stretchiness of the knits. Here are some pics of some I have done.