[Executor]

-You need to optimize blood hunting. Using provinces from around 4k-7k is best, patroling and blood hunting is not so good as you'll kill the population too fast.
You need to spread your blood hunters, I myself, as do most players, use only 3 blood hunters per provinces with taxes set to 0% of course. If the unrest gets too high, which it sometimes will, it's best to let it normalize on it's own rather than patrol. (paroling kills 10 population per every 1 unrest)
-There is a ctr+z command on selected commanders that transfers all blood slaves to the laboratory
-Blood spells are generally not used too often. They are situational since you need a lot of blood slaves to use them effectively and slaves can also be killed in battle, also, most of them are MR negated. You need to figure out which spells (if any) suit you best at that moment.
Horrors can be extremely good if you're facing a bigger enemy, you can direct the horrors by horror marking your enemy. ( if you can cast summon horror you should have horror mark as well ). There are other spells like harm which is excellent for braking enemy troops and forcing them into retreat and blood rain. Combining these three spells for example could make a much bigger army retreat.
-Demon summons are excellent! If you can get ritual of the five gates I'd suggest maximizing it. Every single one of the demon summon is worth their price. Of course summoning demon generals is even better if you want to make SCs.
-Blood items are not that useful actually. On occasion you'll use the black heart to create an assassin or boots or youth to stop old age, but the most common blood item used are boosters normally. Heart finder is also MR negated btw.