Howdy, howdy! Just logged back into my account after a few years and setting up a fresh LSPDFR game so hopefully I can be of some help.
A good place to start is the "Essential Mods" tab under downloads. There you'll see some basic things to get you started and also the Emergency Uniforms Pack: Law & Order(EUP). This will get you a good base for those fancy uniforms. The mod page for EUP will also link a bunch of other mods to use in tandem with it to get the best experience. I'm talking a menu to change uniforms, mods to get your backup to wear the cool uniforms, etc.
The AI dispatch I believe you are talking about is Grammar Police (recommend to use with Radio Realism FR). It allows you to use voice recognition to do a lot of stuff. There are some other resources out there that allow you to expand the responses and such.
For graphics, I use NVE, which is a paid graphical mod. Don't know too much about other visual packs but there's plenty out there.
For more liveries, weapon models, etc... there are plenty here and on other GTA 5 modding resources.
Hope this answers your questions for the most part.