1.LoL it is not about prevention is is about killing them before or after they turn into one it is part of their job to hunt as well mages and abomnations it happened before and templars dealth with such situation even in codex entry one is described... Gregoir needed support because there were many abominations and attack was suprise and by that they were unprepared.When templars hunt mage they prepare themselves and have advantage.
2.By watching them i mean circle most templars is focused on watching mages in the circles and rest on hunting them and yet most mages is captured and draged to the circle.Without circle there won't be need for watching part so anti-mages will be focused 100 % on hunt part what will increase efficiency add to that other measures that i plan use.
3.Nope as it is said abomnation is more powerful it because it delivers power both for mage and demon pretty much reason why mage power adds to abomnation power as well demon power does. Orphanage is single example in fact only one as far not caused by mages with many examples of veil being torn by mages.And it is 1 of 3 ways that demon go through the veil and is rarest way for demon still almost dominated by mages.Other 2 way are only possible for mage to cause first is demonic possession and second is being summoned by blood mage and those are most often reasons why demons is there.Kill mages and it will as i said reduce so critical minimum and even then if demon pass it will be much weaker as it won't have mage as host at worst it will be human mostly rock/tree.
4.Sometimes yes however as it shown it is rarely reason why they reach for blood magic mostly it is power hunger.As i said as far series goes we have only few Individuals that reached for blood mage because of templars and we have a lot blood mages.Simple not true uldred rebelion was because of his power hunger and desire for not being punished for his sinister researches.You mean that power hungry and insane mages in da 2?
5.It is pretty much shows that if i can blow that with magic i don't have reason to found way to do that in another way simple example.Major reason behind technology is to fulfil human desires and needs.Pretty much you if you didn't need to eat or you could just create food with thoughts there would be no reason for technological progress in that matter.As cultures that despise mages or don't have them are more technologically advanced than those who have mages.In fact those cultures are only shown any intrest in technology humans and elves suck in that matter as far we are shown only dwarves and qunari are shown doing something in that matter.
So what im pretty sure that part about protecting mages is there only to look pretty like ban on blood magic in tevinter.As far pretty much only Evangeline have such desire and that was rather because her naiviety.Pretty much that entire order went mage hunt shows that.To be honest i don't care about duty as long they are effective they aren't.True goal of templars was always to protect world from mages not mages from the world.
6.As i said templars have to ways to found mage if they didn't they wouldn't have majority locked up in circles (an as i said that is when most of templars sit in tower and watches mages now we have 100 % focused on hunt part). Sooner or later mage powers manifest when they are young and they can't control that so pretty much to find such person isn't big problem and that most of society hates mages only helps.If spread proper propaganda and tell that things like that mages are evil or maker hates mages it will only help with that.Also laws that will punish those who protect or help mage so it will bring fear for those.Another part is that also offer reward for those who will help capture mage and a lot peoples need money.So we have hate ,religion ,fear and greed on our side and those are most powerful factors that you can use to maintain control.
I love this number format we've got going, makes it so easy to read.
I highlighted my points in bold, it will save you lots of reading time if you don't want to read my novels 
1. It needs to be about prevention. You'll need several Templars to deal with one abomination, its not as easy as 1:1. If you force every mage to turn into an abomination to protect themselves, you'll get most of your Templars killed. Its not as easy as "surpise!" or even preparation, its a numbers battle. Think about what mages can do; firestorms, can you imagine your army being caught in that? You're totally underestimating how strong mages are.
2. I see, all Templars are dedicated to "hunting". I hope you realize if a mage lies low (Like the Hawkes in Lothering) they are never found, unless they transform into an abomination like Meredith's sister. You can't just say "Go hunt mages, all of you!" and expect them to return with one mage each. How are you going to "hunt" mages when families no longer give them up, and phylacteries no longer exist?
3. I don't think you're reducing abominations to a critical minimum when you encourage mages to hide from the Circle and be Apostates. And when you threaten them they'll undoubtedly turn into demons to protect themselves... Don't you see? You're creating issues by trying to deal with them. Abominations would be more common then ever, because you leave them no other option.
4. Uldred lusted for power, sure. But remember that Blood Mage woman who you could talk to in the tower? Most/all the mages following Uldred were in it not for power, they were just trying to free themselves from the Circle. Most/all I said, you see? They just wanted to be free, they didn't care for power after that. Same with Jowan; he used it to make him stronger so he could escape and be with Lilly. He didn't want to be all-powerful.
5. I think you misunderstand how powerful abominations are; they're not simple melee creatures like DAO, read the part with Pharamond in Asunder. He kills everyone in the Fortress and raises them as undead. Gameplay does not = Lore.
Mages need to be protected. Please look up "DA2 Olivia" on the wiki, see what happened to her. if mages are not protected from the commonfolk, they protect themselves. Either with normal magic or demons, either way you have more violence and death happening because Templars were not there to diffuse the situation like Evangeline did. That's simply a fact.
6. They don't just "find" mages. Families send their children to the Circle because they know the Circle will educate them. Some families don't do that and keep their children (The Hawkes, Meredith) but thanks to your plan, what family would give up their child for certain death? Would you do that? Most wouldn't, now you've encouraged people to harbor apostate children. Which means some of them will turn into demons, some won't. Either way, the problem is not gone; mages are still out there and you won't find them until it is too late.
"We have hate, fear, propaganda, greed on our side".... I'm sorry, I thought the point of this thread was to improve Thedas. You're basically becoming as corrupt as Tevinter now. You're lying to your people, threatening them if they want to protect their children, and rewarding people for essentially executing their children. And you're making the world a more hateful place. Think of the false witch hunts, and how many innocents will die because their village suspects some old crone is a mage.
Also, I hope you realize mages cannot be tracked unless Templars carry the mages phylactery, and since you're killing mages on sight there is no chance to make these anymore. So dedicating 100% of your Templars to hunting won't make a big difference.