It sounds like you or your dept needs to put a committee together with supervisors and FD Administration to come up with dispatch protocals for your dept.
But let me offer some help here pertaining to your questions.
#1 Odor investigation outside, 1 engine, inside will depend type of odor, gas order, 1 engine, if you have patients overcome, then send engine and paramedics and ambulance.
#2, Gas leaks inside, maybe 1st alrm response, 2 engines, 1 truck, Batt Chief (With CO meter)
#3, gas leaks outside, single engine response
#4 rescues, closes engine or truck company along with paramedic unit and ambulance
#5 CO Alrms, refer to leaks, inside with either single engine or 2 engine and paramedic unit and Chief with CO meter
#6, Explosions, a full 1st alrm response, maybe 2 engines, truck company, Batt Chief, depends how large your dept is for equiment, you can never overkill a response, but you can always cancel a unit.
#7, fluid leaks, single engine company, gas tankers, full hazmat response with 2 or 3 engines, paramedic and Batt Chief, Hazmat unit, Foam unit, again depends on equipment availabilitiy, you can always go with mutual aid requests.
#8, smoke investigations, 2 types, inside, full first structure response, outside single engine.
#9, non medical response, routine type calls, single engine or truck company, depends on needs, but remember this, TRUCKS usually don't have a water tank, Quint type truck do have water tank, Never under estimate on sending an engine company, they have WATER :)
I hope this helps, If I can be of any other service feel free to contact me directly
Pete92808@sbcglobal.net28 yrs experience in FD Work