Right now with the new nerf of illumination, i decided to gear up a fair amount of int and mp5 to maintain my mana pool while healing. I'm not sure if its the right thing to do that's why i'm seeking advice. Like, what stats should i prioritize? Should i just ignore mp5 and continue gearing up int? Can i start healing the first few bosses of Ulduar25 with my current gear?
At your point just focus on upgrading the blue pieces. As you gear up you'll get a feel for what you need gear wise.
And yes you can start healing all of Uld 25 sans hard mode for that matter, its really easy.
Generally, MP5 comes on the gear. I don't gem for it, but others do to meet their meta requirement. Go for int, as not only does it increase your mana pool, your crit, your sp, it increases your mana regen. When you pop divine plea, you get 25% of your mana back over 15 seconds. The more mana you have, the more you get back.
Also use seal of wisdom and stand with the melee on the mobs for the seal of wisdom weapon hit procs, and you will get mana back. I get around 1121 per tick in raids. Also judge light on each cooldown, as it counts as a melee attack and returns mana. Using proper cd management on Divine Plea and proper placement, MP5 is less of a worry.
Prioritize Int, SP if you plan to spam FoL, haste is meh but you need some. Seals of the pure give you 15%, so aim for at least 10% haste so you're sitting at 25% after judging. I run just under 2k sp myself, but after procs, 2117 so aim for the 2k mark for sp and you'll be fine for mostly HL, FoL, I think they try for around 2200-2400, haven't done that for a while myself.