ARB makes a great front winch bumper for a mini. For a rear bumper with tire carrier I would go to these guys:
Kennesaw Mountain Accessories
A word of warning, they are very slow as they build to order so lots of patience may be required. I have one of their rear bumpers without the tire carrier on my 85 4Runner and am very very pleased with the quality and the price was very reasonable.
Everyone has made some very good suggestions but there is a blurred line between rock crawling and expeditions. For example, per my definition of expeditions, dual cases would be a waste of time and money but I'm sure others would disagree as their definition would differ.
You really need to decide what you want to do with the mini and go from there.