Firstly, congratulations on completing your PhD. This will put you ahead of many looking to enter the consultancy arena.
To answer your questions:
1) If you are thinking about seeking employment with a Big 5 company, then as with most things there are 2 sides to the coin. On the one side many consultancies are reducing the admin. type support functions that support their talented consultants in the field. In many cases its last in first out.
However, on the flip side, many blue chip (Fortune 500 / FTSE 250) companies are looking to outsourcing as a way of reducing their operational spend, in an effort to remain competitive and survive the current econmoic downturn. It would seem that, many big-name consultancies are being drawn in to more new enquiries than ever before. But its a buyers market and they are having to bend over backwards to demonstrate greater value for the clients money.
You may also want to think about freelance consultancy. Again its a tough market right now, but depending upon your commercial experience and skills focus, you find this to be a better choice - at least for the moment. Its worth talking this through with some of the headhunting / interim agencies, and also some of the I.T agencies.
2) This depends largely on who you talk to. Often an MBA is more of a need to have than a PhD, but again this can depend upon the industry you have targeted to enter. The heavier industries (such as chemicals / petro-chemicals) often prefer PhD graduates to an MBA. It often depends on what you want. It would be worth approaching some of your desirable employers and askign them directly what they would prefer to see, and how they perceive your skills and qualifications fitting their requirements. They will soon tell you if you need to do more before they consider your application.
You would also do no harm by getting involved with a couple of trade associations specialising in your field. This will help to develop your contacts network and help you to understand more about the entry requirements to your target industry sector.