Chainsor

Kewl, glad it is working for you 🙂 If you want a police uniform, you have a couple options I know of off the top of my head. You can either go to a police station to go on duty, instead of doing the ForceDuty. This will allow you to pick a new police character, as well as a police vehicle. I use the EUP mod and created my own character and put one of the police uniforms from the mod on, which IMO look better. I'll throw ya some links:
 
 
 
They also have another pack for EMS and Fire
I am going to say it is NOT normal for all the cops to show up and try to kill the suspect.... at least this doesn't happen for me. I, however, also have never played with just vanilla LSPDFR so it could be one of my addon plugins that make things work better.... Maybe try LSPDFR +
As for your 3rd question, I can only recommend just playing and learning. Can't really go over EVERYTHING here lol. Basics are just playing the role of the police officer lol drive around, pull people over, respond to calls, ect.

First check here https://ragepluginhook.net/Downloads.aspx
Make sure to grab the newest version of reagehook plugin, the one included in the LSPDFR installer is not up to date. Didn't mention if you've done this already so just wanted to make sure.
 
Have you gone into the options when launching ragehookplugin by clicking the little gear symbol and then the Plugins tab, make sure LSPD First Response is set to load on startup, or if you don't want it to load on startup, you can open the console once the game is loaded and type ReloadAllPlugins. (there may be another way but this works for me). Once you know the plugin is actually loaded up, you should see police stations marked on your map, you can go there to go on duty, or as you mentioned, in the console you can just type ForceDuty.