Here is a link that you can go to that has information for embroidering on different items.
http://www.emblibrary.com/el/elpr...
Starting with redwork is a great idea for t-shirts until you get the hang of it. When you do start doing fill stitch designs remember you may need more than one layer of stabilizer. I heard some place that for each 10,000 stitches you need another layer of stabilizer. Go by the stitch count for the design to determine the density.
When I do t shirts, I make sure I do NOT hoop to tightly. The design may distort.
Good luck!
Hugs, Bonnie