This Sultan RS Police Interceptor might save you a heap of work (otherwise you'll need to learn how to use Zmodeler3 to create your own vehicles, no small undertaking for someone just starting out)

That Sultan RS Police Interceptor is set up to work as a dispatch vehicle ('vehicles.meta' flags 'FLAG_LAW_ENFORCEMENT' 'FLAG_EMERGENCY_SERVICE' added etc), has a 'template' texture in the '.ytd' (so you can edit that to make it look however you want etc) & contains pretty detailed instructions on how to install it using a 'mods' folder (always install to the 'mods' folder, never overwrite vanilla files, that way you always have a vanilla copy of any file you edit to revert to if needed ).

How to use the Sultan RS Police Interceptor as a dispatch vehicle:
All you really need to do is install the add-on as per the 'Readme.txt' instructions ('dlclist.xml' info can found here), edit the template texture if you want (maybe reduce it to 2048x2048 also, but up to you) & then add 'policesultanrs' to 'dispatch.meta':


Replacing the name of one of the police vehicles already in there will be the easiest option

'dispatch.meta' '<VehicleSets>' Example:

<VehicleSets> <Vehicle> <Name>POLICE_CAR</Name> <ConditionalVehicleSets> <Item> <ZoneType>VEHICLE_RESPONSE_ARMY_BASE</ZoneType> <!-- Zancudo Military Base Dispatch Vehicles--> <VehicleModels> <Vehicle>crusader</Vehicle> </VehicleModels> <PedModels> <Ped>S_M_M_Marine_01</Ped> </PedModels> </Item> <Item> <ZoneType>VEHICLE_RESPONSE_COUNTRYSIDE</ZoneType> <!-- Countryside Dispatch Vehicles --> <VehicleModels> <Vehicle>SHERIFF</Vehicle> </VehicleModels> <PedModels> <Ped>S_M_Y_Sheriff_01</Ped> </PedModels> </Item> <Item> <!-- No '<ZoneType>' = City Dispatch Vehicles --> <VehicleModels> <Vehicle>policesultanrs</Vehicle> <!-- 'policesultanrs' replacing 'police3' --> </VehicleModels> <PedModels> <Ped>S_M_Y_Cop_01</Ped> </PedModels> </Item> </ConditionalVehicleSets> </Vehicle>

Be sure to grab a copy of OpenIV & install it's plug-ins (OpenIV > 'Tools' tab > 'ASI Manager' > Install at least 'ASI Loader' & 'OpenIV.ASI') so you can use a 'mods' folder.

'mods' folder setup basics:
Refer to this post for some basics on setting up a 'mods' folder.

That should be most of the basics covered. Any issues/questions give me a shout