Bare bones inquisitor Lord for me.... Just take the Lord, a Power-Weapon and 3 Acolytes with either Storm Bolters and Storm Shields, or Artificer Armour, depending on wether I know my opponent or not... He's survivable, but only there to open up the Daemonhosts option...
However, one concession I do make is if I am going to be fighting a Daemonic Opponent, I take the Grimoire Pandaemonica - making your enemy Reroll Summoning or Possession is nice...
As for the books of pain - the hardest part of the books of pain is getting into the position to use it... Equipping your Lord and Retinue with massive amounts of Firepower to deal with what ever you pin would be the idea, but it has a few fundamental flaws...
Either, A, your Opponent is gunning for you - which means he'll be skipping around 12" right into you in one turn - possibly more depending on units... But regardless, he won't be finishing within 3" of you for you to release it in your Turn...
Or, B, you run right up towards your enemy and stop just in front of them to give them serious Dakka... Sorry, but if your Squad is better off shooting - then don't go anywhere near the enemy - give them that firepower at 24+ inches, since Storm Bolters, Plasma Cannons, Heavy Bolters and Psycannons seem to be the "norm" for Shooty Squads...
Save the points for an Icon of the Just...
As for removing the units.... There's no in-game precident to allow you to do that - of course, it could be argued the other way as well... But simply put it, if you could choose to just kill off your own troops, Then units which endanger your own (the Chaos Dreadie is an example - just a poor one. I am sure there's a better one) could be taken off without damaging potentially even more expensive units at the cost of itself... Not so... Or more importantly, removing units outside of shooting to get the Majority Armour Save right before that AP weapon hits....
Granted, the last thing you could do is take my opinions on Crunch... Fluff is the way to go...
As for the Relictors - I'm a long-time player of them, and when it comes down to it, if your army commander isn't a Librarian of Some Sort, you're not playing to the fluff... Of course, I always called mine a Lexicanum... Looks like he gets a promotion for the new Codex... Best of luck - remember, a Penitent Crusade is the best way to work Directly for the Emperor!