Welcome to KH and to knitting. I think you're gonna love it!
I suggest worsted weight yarn in a light solid color and US size 9 or 10 knitting needles to start. With a light color yarn it's easy to see your stitches and the worsted weight yarn is easier to work with than skinnier stuff. You'll want a yarn that's smoother rather than a fuzzy or bumpy yarn. I'd suggest cheap acrylic for practicing, such as Red Hear Super Saver. It will stand up to repeated ripping out and when it gets frayed you can cut it off and toss it away.
I should never overestimate my basic arithmetic skills.