How easy it is to modify the existing askbot functionality

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I am creating a project where Q & A is just about 20% of the entire site. I haven't started my project since I am still in the research phase. I have gone through the documentation provided by askbot and I am keen on using it for the Q and A.

There are certain additional stuff I need to add: For ex:

1. When a user registers for a first time, a form should appear before him which he needs to submit.
2. The questions should be of sorted by relevance rather than activity. By relevance I mean questions he would have followed or activity of people he would have followed or by something else.
3. How easy is it to modify askbot database tables?
4. Each question will have multiple tag box each box suggesting what he would tag. Ex : tags for subject, tags for company, tags for experience and so on (Just trying to give an example)
5. How do I start? Should I import askbot as my first app and build rest of the functionality around it?
6. I would also like to have "news feed" along with a list of questions when the user logs in.
7. Add more information about the user who has asked a question. Like his comapany, college, etc (I am referring to a image which is seen next to the question)
8. Can there be a hierarchy in tags? Top-level: Computer science, Mid-level: C program, Low level: function pointers. How will it look in the database?

What do you guys recommend? I know its possible to do this but looks more like a hack which could be a pain maintain unless I have a complete grasp on askbot. How easy it it do this and possibly much more. I also would like to contribute to the community if they find any of the additional functionality useful.

Kindly help