Everything Martial Arts Kitten said was helpful. If your friend is well affiliated within the industry and being a 2 time british thai boxing champion he must know of coaches he can take onboard, Or he must be coaching somewhere.
Location, demand for it, advertising your gym, kit suppliers, you will need bags, pads, a ring, mats and only after you've got a location i.e a big warehouse. Also since MAK has set up their own gym, I would be a little bit more appreciative of their help.
2 questions, whats your friends name? And why do they need you to post it for them?
How you expect to run with the wolves come night when you spend all day sparring with the puppies
Martial Arts kitten knows what he is talking about, and its actually a bloody nice gym he has, its only down the road from me and has a good set up there.
Simple things for the business side of things.
Get a decent accountant, A good one will save you more money than they cost. (word of mouth is usually the best way rather than advert in paper),A sympathetic bank manger, A very understanding Misses (or Mr?) as its going to take up your life.
Thats before you even factor in the amount of staff and there level of experience, rent or buy the premises, how your going to pay for it all and is there a big enough target market for you to cover the costs in your area let alone make money!