I, too, wanted to make a Log Cabin as my first quilt. (That was about 12 years ago.) Everyone discouraged me from doing it (every quilt shop I visited). i, too had a hard time figuring out how much fabric to buy. I still have some yardage from that quest. I finally ended up making a disappearing 9 patch for my first quilt. I learned a lot on that quilt. Amazingly, it turned out pretty well.
I still have never made a Log Cabin, but your journey reminded me of my early quilting desires.
bkay