[*]Cast Judgment on cooldown (it generates Holy Power).
[*]Cast Exorcism on cooldown (it generates Holy Power).
[*]Cast Final Verdict (when you have 3 Holy Power).
Now... on here it says cast Final Verdict @ 3 holy power? so, Im a little confused on why it said to use it only when I had 5 holy power above?
Thats where Im lost for FV/Divine Purpose.
I also would like to know the rotation for sanctified wrath/seraphim build. I like sanctified wrath better than DP, but I would like to know how to use it with Seraphim. Please and thank you =)
Try not to use icy veins as the be all and end all resource.
A really good way is to go to WarcraftLogs and find a good ret (try Schomberg from Death Jesters) and go through his cast sequences (make sure you check his buffs to see which talents he is in). Generally if you have an generator up in like less than 1 second, you should wait for it before dumping your HP unless it's like nonproc exocism or something. A lot comes down to getting used to your bars and muscle memory.
While the Icy Veins one is basically correct (allthough basic), you can find a far more detailed and better priority list in the PvE ret thread on this forum.
Also, you have no reason to be confused about why FV should be casted on 5 HP sometimes and 3 HP sometimes, Icy Veins specifically covers HP pooling later in the guide. Basically, you want to pool holy power as much as possible so that you are never in a situation where all your holy power generators are on cooldown yet you do not have enough holy power to use a holy power spender. However, you don't want to pool beyond 5 HP because there is no room for more holy power then, so when you get to 5 HP you prioritize spending HP to make more room.
In fact, from your questions, it sounds like you're reading it as a rotation (why cast FV at 3 HP, it already says to cast FV at 5). It's not a rotation, it's a priority list. If you have 5 HP, you should cast FV. If you can't do anything else, you should cast FV at 3 HP.