1. If I side with the Mages, I use them to save everybody. If I side with the Templars, Isolde dies in the blood magic ritual while I laugh maniacally because I hate her. Connor always lives. It's not his fault his mother is an idiot.
2. With my happy, sparkly, "good" characters, I usually side with the Mages. With my pragmatic Wardens or my more wicked Wardens, I side with the Templars.
3. I have never abandoned Redcliffe (except as a test just to see what happens, and I immediately went back to a previous save). However, after reading what others have said, I might just give it a try.
4. I almost always break the curse. I'm not into the "save the Elves but kill the Werewolves" mentality. The current Werewolves were royally screwed over by a very vindictive Elf for a crime they didn't actually commit (their ancestors did). Besides, Zathrian is a tool, and Shale wants to squish his head. So he can die, and everyone else can be free. I have sided with the Werewolves and killed the Elves one time on a very naughty Warden playthrough. It was... interesting.
5. I've chosen both as King, but although Harrowmont is a nicer guy, I think Bhelen is a much better king, so I side with Bhelen more often than Harrowmont.
6. I've saved it and destroyed it. Happy, sparkly characters usually destroy it, while pragmatic or wicked characters keep it.
7. I always spare the Ashes. I mean, I couldn't give a fig for the Chantry and its teachings, but those things are magical! I destroyed them once to unlock the Reaver specialization, but then I went back to a previous save and spared the Ashes. Magical, healing Ashes of awesomeness? Yes, please.
8. I usually kill Loghain, but I have spared him a few times. It depends on the character. I usually end up developing a respect for him by the end of it, and the "Loghain Friendly Eligible" fix ZDF offers definitely adds some new insight into his character.
9. If I'm romancing Alistair, my character is on the throne if she is a Cousland, and if not, Alistair stays a Warden with me. I am NOT into the whole "mistress" thing. No, thank you. If I'm not romancing Alistair, I usually marry Alistair and Anora, unless I'm a male Cousland, in which I marry her and become King. I've never put Alistair on the throne by himself.
10. I've romanced them all at some point or another. My favorites are Alistair and Zevran for female characters and Morrigan for males, although I've romanced Zevran with males as well. Leliana is my least favorite person to romance. Too preachy for me. On my craziest playthrough I managed to complete romances with both Morrigan and Zevran, married Queen Anora, and had Leliana on the side up until she dumped me because I was marrying the Queen. Juggling three romances and marrying the Queen with the same Warden? Now, that was insanity. I don't know if I could manage to pull it off again. 
11. I usually accept Morrigan's ritual. I have done the US and sacrificed both Alistair and Loghain before (for the achievements), but now that I have said achievements, I usually do the ritual.