My paladin jurney

After many tests with different classes I've chosen to level a retribution paladin.
As I understand it a paladin, in order to be useful to the group, must play a support role beside doing DPS.
I thought to open this thread in order to learn how to be effective in this regard, and to help other new players to learn the same.
I'll try to put here some questions, to which any help will be much appreciated!

1) HOLY LIGHT: I'm watching some ICC streams from ret pala point of view and it seems that many of them don't even have this spell on toolbar.
As I'm near to lvl 15 and will start soon dungeons, I want to help as much as I can. I've installed Grid + Clique. Do you think I need to bind this spell to Clique (or alternatively a mouseover macro)? Would I be able for example to heal the tank in case the healer is dead? What are some other examples where I need to be ready to use this spell in dungeon?

2) PURIFY: As with Holy Light, I don't see this spell in ret streamers in ICC. I know that at a higher level I get Cleanse, but I know that in some cases I can't use Cleanse because there are some magic debuff that, if dispelled, can kill the player. Is this more of a PvP scenario? Or is this true in some PvE scenarios too?

3) HAND OF PROTECTION: I know that the recipient of this spell can't attack or use physical abilities. I know that the buff can be cancelled but I suppose that especially at low level not everyone has /cancelaura macros, so I need to be careful when I use this in order not to make more trouble instead of help. As it says "attack or physical abilites" I suppose this penality doesn't apply to healers, so there's no risk if I use it on the healer? Is there anything more I need to know about this spell?

4) RIGHTEOUS DEFENSE: same as above, I don't see it much on toolbars on ICC streams, but I think it could be useful for example if a healer is attacked, isn't it better if I take the aggro? Or this is exclusive work of the tank and in doing so I'd obstruct the tank?

5) DIVINE INTERVENTION: same doubts apply. As the target won't be able to take action for 3 mins, I fear to be more a hindrance than a help if I misuse this.

6) AURA MASTERY: "Causes your Concentration Aura to make all affected targets immune to Silence and Interrupt effects". Does this mean that it works only if, in a group with more than one paladin, I'm the one with Concentration Aura? Or it will work even if the Concentration Aura is from the other paladin?

7) SACRED SHIELD: do I need to put this spell always on tank, if he's not a paladin too, as soon as it's not on CD?

About helpful speels, like hand of protection, hand of salvation and so on, what do you think is the best way to use them? Do you suggest to bind them to Clique? To do a mouseover macro? And what about spells like Flash of Light and Cleanse? Am I free to use them whenever I feel it's necessary, or is it an exclusive of the healer?

Thank you in advance and sorry if my questions are so naive! I just want to make sure in order not to be a burden to other players :D

1) No you don't use Holy Light, you will use Flash of Light with instant cast(Art of War). You wont just use it either, you will use it in critical situations - player low+incoming damage, player doesn't have defencive up, too much pressure of healers. More specific situations might be, people in Spikes are in fire, green ooze targets same player twice;low amount of players stacked and you need to top one up so he survives; switching sides on Halion, etc etc. Use it when it's necessary only.

2) You will use Cleanse, in some cases it's your job(Silence from Ragging spirits, Consumption comes to mind). You are expected to cleanse yourself whenever it's necessary. And yes, dispelling carelessly can result in a wipe.

3) You use that when some caster is pulling a lot of mobs(Boomkin+Starfall on some adds is a good example). You wont use this on melee/hunters, unless it's very specific scenario and otherwise player will die 100%.

4) You wont use this at all, unless you are doing something very specific and know exactly what you are doing. If you use this you will taunt 3 targets, one of them will likely be Boss and he will make you go splat real quick.

5) This is used as wipe recovery, use it on healer who is in a safe position, when boss resets that player removes it and resurrects everyone fast. Commonly used for all kinds of exploits, most of which are fixed by now.

6) Aura Mastery is very powerful spell and you will be required to use it in specific boss mechanics. It doubles effect of any aura you are using(Frost Resist+Aura Mastery on Marrogar if people are in flames, Blistering on sindragosa when people have stacks, Shadow resist+AM on First Infest in P2, shadow realm when things start to go bad/healer debuff+corporealty/etc). It even doubles Crusader aura effect, so you can use it for movement boost in world.

7) You will use this only on yourself, it's quite unnecessary in most cases, but there are places where it's worth the GCD, mostly high, ticking damage phases/bosses.

Make whatever way is comfortable and quick to use those spells, Hand of Salvation/Sacrifice/Freedom, Lay on Hands will be commonly used at your judgement unless your raid has any specific times or tactic when to use them.

Wow thank you for the answer! It sounds like a lot of responsability, I hope to be able to do this :D