Internationally difficult question to answer as the technical details may be easy to answer the electrical safety requirements for where your are often individual to your area.
Where i live an electrical engineering company will be employed to design the arrangement of eqipment and an electrical contractor employed to install it to the specification and electrical safety rules. The companies maybe one and the same.
While it maybe vague to yourself, the engineering and installation is often fairly standard, but obviously with anything even design and installation may not be the best and depends on who you use.