Hey Nic,
I'll leave the comments I originally made below. But, I wanted to edit this answer and give you a pointer to an excellent presentation about the Impactjs engine and its use in MMO type situation. Just ran across this in the Code and Games forum.
http://impactjs.com/forums/games/working-on-a-mmo
http://impactjs.com/forums/code/impact-tutorial-here
http://www.youtube.com/user/hallsofvallhalla
If you read the links and watch the videos, you will get a very good idea of what is possible AND what it will take to make it happen.
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I'm still a bit new to the Impactjs engine myself. Enjoy it plenty. But I haven't ventured into the outer darkness with the engine -- just simple single player, no persistent data. So others may definitely give you a more educated view.
That said, here's my take on what you are asking.
The Impactjs engine is a very fine engine for HTML5 client-side games. The kind of work that the engine does for you is calculate collisions & movement. It will provide a very organized game turn with movement, collision, damage, death, and other standard functions required for a player character to "walk around" inside a level.
Impactjs has a nice built in loader and debugger, etc.
It is written in javascript. Which is exactly what you would expect for a client-side HTML5 game.
Client-side means all of the functions that happen on a players computer.
Most of the functions that you mentioned in your question involve server-side functions.
Quests will require a persistent data system better than cookies.
Guilds would require not only persistent data, they would require an admin screen for you to make changes, edit, and generally maintain the guilds.
As far as "simple account manager" goes, I don't know of any. There may be simple to use account mangers true. But the job that an account manager does is non-trivial -- especially if your game becomes popular and attracts any of the usual account meddlers that plague Steam and pretty much every online gaming system.
In order to use the engine you will need to learn javascript at least.
But then when you communicate between your program and a server you will need a second language -- or at least a different headset to work with the added complexity of using client-server protocols.
There are some excellent plugins that people are making available -- that work with Impactjs engine. But you will still need to know some programming in order to make it work.
You seem to have a strong vision of what you want, and have some drive. No matter what gaming engine you selection you will either be forced to learn some programming yourself -- or, you will need to buddy up with someone that does program. You can buddy up by being partners/friends or by $$$.
I just don't see getting by in the game development area unless a programmer is involved.
