@ 1) Depends on how much you go over-cap. If you don't over-shoot it by much, go for it.
@ 2) Glorenzelg is actually the better pick for competitive PvP. If you're not doing top-end PvP, then it doesn't much matter which weapon you use. Oathbinder will have stronger damage, but Glorenzelg has stats that help you survive more.
@ 3) For PvE, the agility ring is slightly better. 20-25 dps difference, iirc. You won't notice the difference though. If you PvP, consider keeping the strength ring for more AP.
@ 4) Agility socket bonuses aren't worth it.
@ 5) Death's Choice is better for PvE and casual PvP. I recommend Whispering Fanged Skull for competitive PvP or if you off-heal a ton as Ret (the crit helps get Art of War procs, and helps your heals crit more often). WFS is better than DBW, Herkuml, and any trinkets from any content below ICC with the exception of Death's Choice/Verdict.
@ 6) Both builds make great use of Shadowmourne. You're currently using Oathbinder, so there would be no issues. Someone that uses Glorenzelg would need to change their build and/or glyphs to make up for the lost expertise though. I currently prefer a full strength set, with the exception of Umbrage wrists, due to not needing hit on that slot and everything else is just so much lower dps value.