One small but important detail I left out: Break the yarn when you finish the first strap.

Increase row should say:
K1, M1, K2, M1, K1 (I’ll correct the download when I get a chance.)

Gauge: I don’t know. It’s unimportant. Don’t bother knitting a swatch for something so small. If you see you are making straps narrower or wider than you like, you can easily adjust the number of cast on stitches to achieve the look you want.

There aren’t a variety of sizes included. You will need to check your fit as you go. But that’s very easily done. I winged it the first time I made this pattern and when my strap length was too much, I measured how much excess was in my hand and redid the straps accordingly. Got it right the second time.

This isn’t a hard pattern but because exact instructions to knit a specific amount of rows to achieve different sizes aren’t spelled out, it might not be ideal for a beginner.