First off, it's not a matter of smart
, and don't be surprised if someone changes the title of your thread.
Your learning a new language here, and smarts has nothing to do with it. It's just a matter of experience.
First of, there is stitch gauge and row gauge. Stitch gauge is the width--how many stitches per inch you get working across. This is the important one.
Row gauge is length--how many rows you get per inch vertically. You can adjust this by knitting fewer/more rows, so as long as your stitch gauge is ok, you can fiddle with the other.
Most patterns have you knit for X amount of inches, so just go with that on the length.
Straights are fine, many people use the circulars as straights. You wouldn't knit in the round on circs unless you want a tube, which I don't think is the case.
You're doing fine, hang in there.