I always admire your willingness to leap into dressmaking, improvising as you go! I feel baking is similar - as you make bread, use different flours, recipes, you begin to develop a "feel" for how things might work out. I don't experiment a lot with breadbaking, I just need bread to eat :D, so once I Have found my basic recipe, I stick with it and just add extra flavourings.
I found this video yesterday - she talks about her experiences with sleeves ... they are her bete noir. I meant to note the time that she starts talking about it, but I forgot. You can skip through with the slider until you find the part where she starts talking about the blue and white shirt.