Welcome to the board. You have asked some good questions and have received some thoughtful answers. I would take a beginner quilting class so that you can become familiar with all your tools and all the terms you will encounter. You will learn about fabric, grain of fabric, and lots of other terms. Do a simple pattern where you will learn most of the things you will need to know. I would not begin with your sentimental clothing. Wait until you have some experience under your belt. Find a local guild to join also. Their advice and fellowship will be priceless.