Since you will be joining the squares after they are knit, the cast on and bindo off won't show, so the important part will be making sure they are loose enough that they don't pull in the square.
You may want to aquaint yourself with different seaming methods though. I like Annie Modedesitt's tutorials here:
I'm not sure how many squares you've done, but I think you could save yourself a lot of sewing if you worked columns of squares without binding off between them.
In other words, Knit a full square, but do not bind off, Start the next square with the stitches left over from the first, but switching yarns or stitches as necessary.
In this way, you'll only have to sew half the number of seams at the end of the project.