Hello there, thanks for your interest and your post. This presents me with a very different viewpoint that I am admittedly largly
Some interesting ideas you have there, perhaps in the future I could give some consideration to the implementation of some of those, but for the most part, making those work on a DKPSystem.com site will require a bit of hack-approaches.
Now, to address a number of your points:
1) You can already register with an account, and then attach characters to your account. From there you can define which character you wish to be your "Main" but that doesn't serve much of a functional purposes, merely aesthetic.
2-4) Unfortunately, at current, these aren't possible. While each post will list your character's and links to their character profiles, the post itself doesn't have a "character" associated with it. But, like I said, this provides me with a different perspective, and so I can give some consideration to the implementation of such.
5) This is available, to a degree. As I said previously, each post will list all the charactes associated with the account, as shown below:
6) If you sufficiently trust your members enough, you could implement a "kinda" version of this with Guides and give them access to modify them as needed, but there'd be no central "Quests" page, per se. You COULD, however, try utilizing the "Keys, Attunements and Completed Quests" functionality to be something to this effect, but ultimately, anything you'd do here would be some wierd hack. You could ALSO try to implement a "Quest Page" by perhaps utilizing some hack of the DKP System. Perhaps creating a bunch of "DKP Raids" on the same day with different names like "Quest X." Then, if someone completes a quest, they can inform you, and you can then go to
Admin > Raid Attendance, check the box next to their name for the appropriate "Raid," and in their character profile, it'll show as completed. It would be twisting the Loot Systems in a completely unique way, but I see it working. The addition of the "I was there" link provided to members would make this "Quest completed" thing fairly smooth.
7) If you do any of the hack approaches listed in 6, you could easily attach an image to the summary for you. That'd be trivial.
8) This, being the most general request, is pretty hard to meet properly. You could simply say in the text that "completion of this quest will earn you X or Y."
I'll admit that the site isn't terribly conducive to RPers, at least in the areas you describe, and historically, it's built around making a raiding guild a well oiled machine. I will say that some of the tools provided on this site are flexible enough that with some creativity, the functionality could be twisted a bit beyond it's original design (like the DKP hack I proposed above), which would, in a sense, emulate what you're trying to do, to a degree, but at the moment, most of what you've suggested isn't supported directly, via something like a built-in "Questing" mechanism.
The more I think about the Questing mechanism, however, the more I realize that building something to that effect isn't exactly hard, per se.
I'll stick member-defined quests on the list and see when it could be implemented.
Thank you for your feedback, this post of yours could help us both: Help you in that you won't have to code your own solutions to this, and help me in tapping the RP market