With all respect here, we do help where we can but under the circumstances of what you are asking and the obvious safety risk associated with such work I'll have to say that the only advise we can offer here is to get a registered industrial contractor on board who is competent and has the paperwork to work on such installs, I personally over my career know of 1 death and 3 serious injuries associated with spray booths all down to breaches in regulations and the forum wouldn't be seen to be giving good advice in offering information on such an install where it is clear by your profile you have no electrical qualifications.
You also need to consider the fan itself needs to be rated for this kind of installation and if you are willing to pay the very high costs of this equipment as with any electrical equipment within the booth as you suggest then I cannot see why you cannot contract in a professional here.
There are regulations that govern how extraction equipment, monitoring and controls associated with said spray booth, we cannot advise without knowing your set-up which may suit a particular type, there are a few methods available but most are a closed loop control system that looks at air content or even at the spray gun been lifted off the hanger to initiate full speed from a low speed idling, when you have manual control a certain element of human error is put into the equation and this can be costly as what you believe to be the correct speed may in fact be allowing a build-up of explosive gases/particles hence you really need to employ the correct people to either do the work or advise you and check the work during the install and before use.