While I agree with redshirting more because you can always take the redshirt off, I have to make a comment on the above quoted part.
If you're operating your team properly, you might redshirt a few upper classmen in the first few seasons, however... you should try hitting as many frosh with redshirts as you can.
I don't always redshirt freshmen simply because I often times promise "No redshirt freshmen year" and then simply redshirt them as a sophomore. Then I get three seasons of play out of them, redshirt sophomore, redshirt junior, and redshirt senior. The only people who are even really playing as redshirt sophomores are receivers and defensive backs in sets which use a lot of those players, or they might be my third or fourth RB (which in my system, will get plenty of touches).
Set your depth chart first.
Anyone who looks like they'll never see the field, redshirt them. If it doubt, redshirt them.
Just remember that if you want them to come in, you can manually take the redshirt off. If someone gets injured, you can put them in and remove the redshirt, HOWEVER also remember that if someone gets injured and you don't MANUALLY make the change to remove the redshirt, the computer will put a non-redshirted player in, which is usually a bad idea if you don't have enough depth there.