Wow! What questions!
Putting them aside for the second, I can really suggest you consult the Vault Career Guides. They will be able to give you much more information in response to such broad questions than people can on a forum like this. But:
1) Substantially. Whilst there are some skills held in common (e.g. client-focus), the total focus of the job can be completely divergent. Both 'IT' and 'Business' consulting are broad areas - can you redefine the question slightly?
2) Again, depends on the type of business consulting and the type of company one hopes to work for. There are grad positions, postgrad positions (either MBA or other degrees) and industry hires - some companies use a mixture of these, others primarily focus upon just one or two of the entry routes.
3) Nope. It probably helps at the higher levels. But, as mentioned above, grad (BA) and non-MBA entry routes are possible.
Sorry to be wishy-washy - you must understand that entire books have been written on these questions!