questions 1250pt list tweaks

[Darigaz]

Here is my 1250pt army I need some help with. I have a LOT of questions. LIST AT THE BOTTOM! 

I am debating whether or not I should run cogs in this set up, and if I should forgo a hero to run more troops/battleline? 30 Chainrasps is all I have right now (would like 40, but we are house ruling x2 squads of 15) and I'd like more than 10 reapers (I think?) I just can't figure out which Hero to cut or if I even should cut one.

I also have Lady Olynder but she is just so many points for this list.

Should I cut a hero and add 10 more Chainrasps?

Would Chromantic Cogs be worth this smaller point value list?

Will 10 reapers be enough table presence?

Which hero would you cut and why?

How come I cant put a relic on Grimhailer?

Which units in this army would you leave in the underworld to deploy later?

Do I need more Wizard?

I have banshees x10 in the wings too, is there a place for them in this list? Clearly I'd have to swap something out. My opponent lately has been a friend running 3 wizard heros in a Slanesh/Chaos list (Ogre mage guy with 8 wounds) with lots of summoning so I figured Banshees would be nice to counterspell him.

I hear Nighthaunt is an absolute monster at this point value.

Thanks guys!