You get a large amount of defense from that rune. So it allows you to require less from gear. The rune will add a flat amount to your defense value on your character sheet, so you won't need to calculate anything.
As for what weapons you should use, at lower gear levels, you should use slow speed weapons. This gives you greater threat. Unfortunately, in this expansion, all tank weapons are a fast speed. So you will have to go for agility weapons. When you get better gear overall, you can start to ditch slower agility weapons for tank weapons, if you so choose. This is a threat loss, but the stats you can gain off the tank weapons can be worthwhile. If you need to use a tank weapon for stats (defense, hit rating, expertise, etc), put it in your off-hand first. Your off-hand weapon does less damage than your main-hand weapon will.
As much as I would like to advise you, Frostwolf is a Mists of Pandaria expansion realm. This guide is for Wrath of the Lich King. I also have very little experience with this class in Mists of Pandaria. As such, I an unable to assist you in the way that you'd like.
Check out this sticky thread: http://forum.warmane.com/forumdisplay.php?f=121
The links tagged with "MoP" are the ones you will want to check out and ask questions on! Good luck!