Oh, since I know that could be sort of problematic,
I won't take my chances... not in my first PT anyway. My first self-insert PT in DAO was with a female Cousland, and that's what I'm gonna pick for my first DAI PT. No troubles with the Amells at all.
Btw, I have my moments too, for sad stories. 
Weirdly enough, I got interested in Cullen the same way you did.
The difference is that I was already interested in Anders, and I happened to play a female Rogue (also self-insert) who left Bethany in Kirkwall, to be safe. So, when Cullen arrested Bethany and took her to the Circle, I was very angry with him for a while.
......until I realized how much I actually liked him.
Later, I would go back to DAO, and install mods and play the mage origin. My first mage origin was with a female elf (also self-insert
). Then, in my second DA2 PT, I planned to Rivalmance Anders (Friendmanced him in the first PT). But now I was crazy about Cullen, and I would spend hours snapping screenshots with him and my Hawke. At times, I would remind myself: "hey, you're romancing Anders! taker your eyes off Cullen!" 
Oooh quite same, my self-insert PTs are usually the first one I played. For DA:O it's Queen Cousland with Alistair, and for DA2 it's Marian Hawke with Fenris (mage Hawke). When I played these two PTs I always thought "this is my headcannon" but actually when I started roleplaying, it seems that finally I can't have any other headcannon than a female mage Amell sacrificing herself (romance Leliana) and a male Warrior Hawke forced to choose a side (mages) because little sister is in the circle, romance either Fenris or Merrill.
I had finished DA:O for all mages & elves origins, with happy/sad ending each. But I can't just bring myself having other headcannon than the one I mentionned. Dunno why. It's just at first I would like to be from the best priviledge ever (Cousland), with loving family etc but finally the mage one really enthrall me. Being a person that is considered dangerous by the world, yet rise above all to be the Hero of Ferelden. Without Old God repercussion.
Finally, my favourite origins from DA:O are the "opressed" ones: City Elf, Mages & Dwarf Commoner. They started with nothing and end up being the Hero of Ferelden, above whoever hated them for what they are. It really proves Dumbledore's point about the most important thing is not "What you are" but "Who you are".
Well they have said there is gameplay once the 'ending' has been done so we know there is at least one chance to keep our inquisitor alive. I don't mind sacrifice endings of different sorts as long as there is once chance for a happy ending, so this gives me hope
But so help me if a LI needs to be sacrificed there is going to be trouble! lol
In one of my PT a romanced Alistair didn't give me the option. He just went on sacrificing himself no matter what if you bring him to the ARchdeamon without Morrigan's ritual. Had to leave him at the gate of Denerim to prevent this happening. I can see this kind of situation repeat itself...