(Disc) Priest / Mage tactics overall, helps

Hello, I'm trying to play disci/fmage on blackrock, we are both new at this setup and sometimes we have no clue of what to do in game. Please don't start with "faceroll setup" or similar, we want just to improve by playing a different setup for one time.

1) First thing is we are both full starter gear, does this hurt our gameplay or we should go fine until X rating? (what you think is X rating?) Priest is going mp5/spirit offset + resi/mp5 gems and mage haste offset + spell pene/haste gems. (Should the mage run with double solace?)

2) I always thought any priest (shadow/disc) + mage was a strong (and maybe faceroll) comp, that have potential, huge ccs, and most of all have dominance over every hpal/war. Actually we lost many games vs hpal/war and hpal/dk. Is the comp still strong, or we are just playing bad?

2) We checked ladder just out of curiosity and there is literally no disci/fmage in 2v2 in top 100 of blackrock, only few shadowp/mage and the highest is at about 2100 while the rank1 is a hpal war at 2800 (which should pretty much loose to every priest/mage... or am i wrong?). Our theory was that if the best shp/mage can't pass 2k1 it means that they reached the rating limit, and they can't beat people over that, so if some 2k5-2k6 pr/mage are stuck at 2k1 there is something wrong, and there's no chance we can climb ladder compared to them, is this way of thinking correct? We checked last arenas from them and they are old 2 months, I doubt they are sitting for titles, 2k1 gives nothing so maybe they simply quit out of frustration? I don't know.

3) As Priest I don't see any mana problems or healing problems overall, i suffer warriors a lot ofc, specially ones with istant overpower 0.1cast and bash at 0.1 before end cast (script), I don't even bother finding tactics for that since the game is already on their hand and I always get two-shotted even without a bladestorm.
My mage, can do CCs pretty good I think, but even after 3 poly, 1 fear, 1 deep, 1 silence on the healer, we can't land a kill on the other guy (maybe we can force some cd). Now everytime we "burst" the target, I always have my burst rotation ready (holy fire, smite, mind blast, swd...and dots obviously, maybe shadowfiend even) but my mage says hes having difficulties doing damage. Some suggestions?

4) My mage frostbolt cast is 2seconds long so he says can do only 1 cast + 1 frostfire istant (if procced) + 1 lance on deep, and thats not enough for us to kill someone (keep in mind that i always burst with hf/smite/etc to help him), seems we can't pressure much. Can someone explain how to best dps as mage and how should be his gamestyle?
He complains mainly about the 2seconds cast Frostbolt (max rank) which he thinks it's the main source of damage, but he can't manage to cast that and make pressure, because 2seconds is too long and everyone can go behind a pillar after dispelling the rank1 frostbolt casts that he spams, he says. I told him "maybe you should manage more the snares and cast 2sec frostobolts only when u are sure u wont get LoS'd, in this way we can make pressure. He says also he can't double nova because one guy is on the left, one is on the right, or the healer keeps hugging the pillar while the dps keep pressuring him in the middle, slowing with pushback every cast and negating everything to him with interrupt, death grip, silence, freedom/dispels from the healer and so on.. the result is a mage trying to snare the melee but the melee gets istant dispelled, he can't control the healer because he keeps pillar hugging and self dispelling r1 bolts, so my mage its like a tank taking huge hits in the middle and doing few pressure (this happens with healer+dps obviously). I also told him to manage better mirror images and pet but honestly mage is not my class even if I know its spells I can't help him with suggestions because I have no clue about how to to damage properly with Mage. When it comes to mana burn party we can oom someone (and i don't like much to play this mode), but after that, the oom guy keeps "tanking" while we spend every single spell to keep him oom + damaging him, and again, we don't know how to make pressure, he doesnt die, most of times we oom more than him...any tips?

5) I suggested some tactic like "you rush on the right trying to nova + CS/deep + poly, I rush on the left with Psychic Scream" it doesn't sound bad to me and actually we managed to do that good but my Mage isn't sure about this and he is always like "whats the point i get kicked everytime, i need to fake 30 times, also he gets freedom, he gets dispelled, oh the healer LoS'd me, I can't do anything and my main damage is a 2sec cast which hits for like 3-4k, theres no point in playing this setup it can't work I can't do pressure".
I saw mages doing 100-0 on a deep, mages doing 2vs1 (like destro warlocks), so I don't think it can't work, maybe we are just missing something imho. Also the fact that r1 pr/mage is only 2k1 and priest is shadow pretty much triggers him. I'm trying to convince him to have some patience because we can't learn a new setup and pretend we mastered it after 20 arenas at, but he just gives up, because everything seems impossible to him.

So, sorry for the long post, I'm asking if you have some good advice for both me Priest and my Mage (what to do, what to not do, how to burst, general tips..)

Thanks :)