In reply to M.Allan: Hi there. It depends on the wall. You may not need to have a SPA or a specific climbing qualification as such. Some walls will train you, in house training and they will provide further courses like first aid, working with kids, sports movement, etc. Obviously, some walls are more advanced than others and budgets will impact the training and what they expect from their coaches.
I suggest you decide where you want to live and work, then contact the gyms in the area as to their requirements. As a self employed coach, you'll need insurance and that may only come if you have your SPA, not sure though????
An SPA is very useful if you want to coach outdoors, not necessarily for indoor coaching. But you should be a climber, with good experience. Good experience is relative!!!! hope that helps.