1) I would say update your graphic settings till its fully green... tbh I have mine as far down as I can.
2) If you need help installing Simple Native Trainer ask and we will help, with the els open the trainer (f3) options (top link) Enable / Disable keys (Its on first menu on the right hand side near the bottom of the list) Disable them! Get into a ELS avalible car J and K should work now. You have to do this every time unless you change it in the script hook.
3) I actually have forgot how to install sirens but use SparkIV (Then EFLC or GTA IV) Depends what game you have, there a few helpful videos and BritishPoliceMods and accounts like that have some nice sirens avalible. Even google GTA IV Sirens..
Need help? Ask, PM