I've never used the thumb method - I've tried, but my brain doesn't think that way, at least from diagrams; perhaps if someone showed me I might get it. It always seems daft to have to estimate the length of yarn you need before you start. I cast on with needles, after the first stitch, I knit behind the previous stitch and that seems to work perfectly well. There are lots of ways to cast on and off depending on what you are making, but that cast on, and regular cast off have always worked for me.