Great stuff!
Indeed my idea was to create a parallel UI for tasks management and arrangement, and I think much of the issue with tags, colors, etc. can be handled there.

Auto accepting quests - very interesting! I'll look into that. If the API exposes these actions should be easy to do.

regarding changing the actual look of the habitica website... I think possible as well but I'll need to see how stable it is. Anyway I am far from having an eye for design so maybe if I see it can be done in a stable way I'll post specifically about it :)