What, if any, training / qualification / experience is expected of the clients?

If you decide to go trekking some minimal trekking (hiking, nature walking) experience is always helpful but not extremely necessary for the shorter treks. Some musts are the ability to know your limitations, co-operation and communication kills. A good attitude is always a must. And being respectful to the locals and the environment is also a must. if you are looking to be even more prepared, you could look into a first aid course.