Few AST questions..

[Donarudo]

Noct effects the same skills Diurnal does, so Aspected Benefic, Aspected Helios and Collective Unconscious (at 58).
Benefic is a 250 Cure + 250 Shield. Helios is a 140 Cure + 140 Shield. CU is a 10% damage mitigation for anyone inside it.
Noct also gives you a 5% magic potency buff.
I'd suggest staying in Diurnal for any content you are the only healer in, but feel free to try what you are more comfortable with.
As for MP, I'm sitting at 11,998 in i181.

Curious...I am at ilvl 182 with 13.2k mana. Is your spec split up or something?