I’m sure many others will chime in, but:
1. The single thing you are negotiating is the out the door, on the road, taxes, tags, and everything else, absolutely final, bottom line number. None of the component parts matter because they are subject to manipulation.
2. If you plan to finance, check your bank, credit union, etc., and find out what rate they will give you. Sometimes the dealers have special financing, but the rates usually are higher and they typically use an interest calculation method that results in a higher total of all payments at the end. Dealers make money on the financing.
3. I used to use Edmunds for price estimates. Other people like True Car or Kelley’s. I’d suggest you look at them all.
4. Know your acceptable final price before you go in or contact anyone.