Grand Master of Divination Librarian

I'm mostly asking for 1000pts, but in 2000pts would I take both or still have to choose between the two?

I like Divination for the primaris power, the malediction, and the 4+ invulnerable save spell. I can't see why the GK spells would be worth taking over divination. I understand you can get cheaper spells from an Inquisitor, but I'd rather not take one if I don't have to.

My idea of taking the Librarian would be barebones or maybe lvl 3. Lvl 3 makes it more likely to get the spells I want, obviously.

Instead of this, I'd take a Grand Master. But at 1000pts I'm not sure if his strategy ability will be as effective as the librarian's spells. I'm thinking rerolling wound rolls of 1 would be the best as I can already score with most/all of my 1000pt list. He does have much better stats, though. Is giving him a Psycannon worth it? I could take 2-3 more psycannons for the points (theoretically) on BS4 guys. I was thinking of giving him a sword for the nice invulnerable. What about the grenades and other upgrades?

HQs are too easy to overspend on, any advice? For 1000pt games and higher. I'm not against using an inquisitor, I just need to be convince  

It seems like this question is being answered in your Sector Command (1000 pts) thread

My advice would be for 1000 points and lower inquisitors are your best friend. but if you're dead set on a Grey Knight as your HQ step forward the Brotherhood Champion!