First off, good luck with your shirts, if you have good designs you will sell them! I'm guessing the Audio Video Disco is an auto-correct? lol, I don't remember that from my high school Latin class... Anyway, what kind of blank and what kind of printing really depend on each other, what I mean by that is, if you want to print on polyester shirts vs. cotton vs. blend as well as what kind of designs, will they be just a few colors that can be screen printed? High detail with lots of gradients and/or color that would need DTG printing? Or all-over style designs that would need sublimation? And to answer about what sizes, that really depends on your market, a good way to get an idea is to do pre-sales of your designs. Let your customers know that it is a pre-sale and that shirts won't be ready until X amount of weeks after the sale ends, this can create an urgency to purchase, less waste of shirts if the design happens to not be as popular as you'd hoped, and will also give you a decent idea of what sizes your audience needs most. It's a good way to get started and learn more about your target market. Hope this helps! 
