Use bigwigs, it tells you if it is spellward, bop, or reflective shield.
Correct, the only time you should need to worry about interrupting with a CS is when BoP is up. your rogues should have their pvp gloves on so that deadly throw causes interrupts, which is able to be used during spellwarding, no warding, and reflective shield (as long as they are not dpsing).
I highly recommend having a elemental shaman there interrupting. Talented they have a 5 second earth shock that can be used to interrupt most of the BoP phases as long as the two spells (wrath and circle of heal) are spread out enough. We use a macro (between the shaman and myself) that he constantly spams me telling me if his CD is up or down. If it is down and I see either being casted I CS it and say it over vent. All you should be DPSing is the paladin -- that is it, unless you are mage tanking then dps the mage. There should be 0 real dps on the priest as you will get smited and probably die because of it. Since all of their HP is shared it should not be done. Just keep her on a focus target and use a focus macro to do it.
Hope that helps and good luck.