You might get a little bored with casting on for an entire week! Though you can try all of them out and see which you like better or gives you a nicer edge but you probably won't notice that until you knit some rows. I think the 10½ needle is a good one to learn with, the stitches are larger so you can see them and easily get a needle into them.
I'll mention now that if you knit all rows you get what's called garter stitch. If you purl all the rows you also get garter stitch, so don't be surprised when that happens. The back of a knit is a purl and the back of a purl is a knit you just make them differently depending on which side of the stitche you're working on. So to get a knit fabric that's smooth on one side and bumpy on the other, what people think of a 'knitting' you have to alternate a row of knits with a rows of purls. You might go to the Tips page a look at Demo of a Small project and see how the different steps - cast on, knit and purl some rows and bind off - all go together to make a knit piece.
sue- knitting heretic