The part that blows my mind is that the ritual was one of the dumbest things the reds could do.

 They know for a fact that when Ortega went after Dresden in a underhanded manner a satellite crashed and destroyed everything for hundreds of yards around his house.
That was meant to be an example, so yes they know it wasn't random.

So their great plan is to go after Dresden in a underhanded manner while gathering all of their strongest members and almost all of their weaker ones within a couple hundred yards.
they were not even particularly secretive about the fact that they were all gathering there.  With the senior councils information gathering ability its almost a sure thing that they would find out.
Thats the main reason i think their was some more important goal than killing Ebeneezer.  If their wasn't the red court would have died out long ago from similar stupid plans.

Ok so let's argue the value of the ritual.
* The initiator of the ritual is Arianna, not the Red King.   She needed something public, something dramatic and something deadly.   The ritual was way over the top, but that is what her power struggled called for if she was to overthrow the Red King.   And she probably had the support of a lot of the Lords of Outer Night behind her --enough that the Red King dare not squash it. 

*  The Red King, once Arianna is dead, also needed something dramatic.  It is unlikely he would have kicked off the ritual himself, but if Arianna did  - utilizing the ritual himself makes perfect sense.   So the Red King would not have been in some hurry to end the ritual.  He needed the ritual to shore up his support as well for almost the same reasons as Arianna. 

*  Consolidating all the Red Court together in one place is not that major a risk.  They disabled a lot of the White Council already.  The Lords of Outer Night were no doubt on guard against some kind of magical assault (falling satellite for example) and would not be killed by such an act.   The Lords of Outer Night could swat that satelite out of the sky in an instant.  Maybe the Fellowship could have hidden a nuclear bomb at the site and blown them all up -- but outside of that scenario it is hard to see how the Red Court would have been seriously threatened.   After all, even with the surpise intervention of three knights of the cross, at least one minor god (odin), an army of Kenku, leah, the new winter knight,  and some of the biggest heavy hitters on the council --- the white council was clearly loosing.  And that was without the lords of the outer night playing a significant role in most of the battle.    The conditions that allowed Harry to win were real "threading the needle in the middle of a hurricane" type conditions. 

*  The value of the kills is huge.   Killing Harry and you kill the boogieman scary enough to cause red court vampires to run away in battle -- and whose death would allow the red court leadership to end the premature war now and finish off the council in 30 years.   Killing Eb destroys the most powerful war wizard in the white council and likely destabilizes the leadership of the white council. 

*  Further more, it is possible that the curse would be so powerful that it shatters the wards around Edinburgh when it takes out Eb.  It would take the white council weeks or months to repair those wards.   I can totally see the Red court celebrating victory when they complete the ritual and then spending the very next night attacking Edinburgh.   The vamps are running an a victory high and the wizards are sickened, scared and demoralized.    They obviously could not count on Eb being there, but it would be a nice bonus.  Even if the ritual did not crack the wards, the momentum they would get from these events would probably allow the Red Court to break the White council in weeks. 

So big upside, little chance for downside.   Why not do it.     

I do agree that the Reds should have stationed a lot more guards around the trigger, but remember the logic that Bob said.  Unless you sacrifice a red court vamp on the alter, it is hard to see how the ritual could hurt the red court.   And almost the entire Lords of Outer Night were there to defend the ritual when Harry got there.   

I do agree it was arrogant for the Red Court to create such a weapon that another could take from their hand.  But the United States builds nuclear bombs and there is always a remote chance that somebody could steal one and use it against us.   We still build them because the bombs are damn useful in the right circumstances so we accept the small risk.   At the end of the day, the Reds did not think anybody had a real chance to take their weapon and they died because they were wrong.   

Cult or crazy very likely.   The whole "magic is not real" thing makes that designation very likely - plus many are probably a bit strange.   

Terrorist or gang - not so likely.  If magic is not real, they hardly seem dangerous.  They are a mixture of people from all walks of society and tend to be led by old women (witches) or men (wizards) as these individuals have the most skill.  Very few engage in illegal activities.

Not sure I see the paranet being such a bridge.   After all, it has a very specific mission - magic using humans. 

It could become an organization that offers protection to outcasts or other supernatural flavored groups, but there has been no evidence to date that it has done so.   At best it has semi-allied itself with Marcone and the White court to defend itself vs the Formor.  But that alliance is clearly opportunistic and temporary.   

Well, we know that Mab is going to be looking to take them down a notch, they were attempting to violate her Accords with their backstabbing actions in 'Bombshells'.

I think you are misreading the situation.   Mab is going to take down the Formor because she believes they are working with the Outsiders.   However, Mab is constrained in her actions.  If she can get the formor to actually violate the accords, then she can directly act against them.  Right now she is limited to indirect action like that of Leah in Bombshells. 

Do not get me wrong.  Mab will defend the accords in any case.  All I am saying is that Mab had very good reasons to take down the Formor well before any accord violation takes place.   She is actively looking for an excuse to act. 

What would the council want with territory? All of the WC wizards we've seen on-screen have had a personal domain or area and couldn't really care about the rest. Half the Senior Council seem to have no interests in material wealth at all.

Multiple Reasons
1) Much easier to find and recruit wizards in territory that they mostly control.  This is not a strong reason as the White Council cannot effectively recruit in their own territory.
2) There are wizards in these lands and the white council dominating this territory makes them safer/stronger/more effective.  Many of these would argue for expanding their area of dominion. 
3) Keeping the territory means that some other supernatural races does not have it.   That means some other supernatural race is not getting a lot stronger and thus a bigger threat. 
4) Status

The scions similar to the talented practioners, they are straddling the line between the mortal and supernatural realm. They both could be seen as mortals marked by the supernatural. Full wizards are far more seperated from the mortal world.

I would instead state it as follows.  Scions are mortals who share some supernatural traits with their supernatural parent, but still retain the mortality of their other (human) parent.  Some like half fey have the ability to become fully supernatural. Others are always going to be in that half state.   

Kazimmoinuddin is correct that many are probably more comfortable with technology that a powerful wizard as few supernatural races have a problem using technology.  However, I suspect many scions have other issues based on scion status such as unusual appearance, cravings, allergies, crazy relatives, etc.   There is no source of power in the Dresden world that comes without liabilities. 

The act of creation was at the point where Harry was held fast by the will of the Outsiders in the Grotto and Lash sacrificed herself to allow him to act.  It was her one act of selfless love -- and thus the spark of creation in this matter.  Whether Uriel helped or not is irrelevant in my mind.  She choose.