Having worked in the insurance industry my entire career, mostly on the client service side, I will try to offer what I can here.
1) I totally agree with going to a Ford dealer with an on-site body shop. They may not STOCK the parts, but they will have access to them. They are going to be able to give you the most accurate (and probably the "highest" estimate). That is your goal, if you are looking to total it.
2) the diminished value end of it is really only relevant (financially) if your insurance company doesn't total it, your insurance company doesn't offer enough to cover the supposed diminished value and you then choose to pursue the other driver/insurance company
3) I am of the opinion that you should always work with YOUR insurance company first, as much as you can, until you can't get anywhere anymore. Your insurance company, when it comes to repairing the vehicle, isn't looking at comparative liability, etc. (That is, it's irrelevant who did what--it was damaged in a collision, it's covered, now we decide the cost to repair). The other guy's insurance company, OTOH, is not only going to battle you on the cost of repair, but depending on your state laws, could argue over the comparative negligence of each driver.
Yes, I realize it's silly to think you may have any negligence at all (and you probably don't have ANY), but the the truth is, that isn't going to stop the other insurance company from at least looking to see if there is any.
4) DO NOT go to the lawyer until you absolutely must. You may say "ah, you insurance guys don't like lawyers". No, we don't. Here's why: Once you are attorney rep'd, we can only talk to the attorney. Then, whatever the insurance company does pay, you stand a VERY good chance of whatever "extra" you think you received has been chewed up by either the lawyer's hourly fee or the contingency fee. You can get the same result by "acting like a lawyer"---standing your ground, making a reasoned argument and not giving in until you are satisfied. That said, if you can't get anywhere with the insurance company, THEN absolutely, get the lawyer.
5) the opinion of the police that the vehicle is "totalled" is ridiculous. They are not: insurance adjusters or body shop employees. Neither your insurance company or the other guys will take that into account. The only thing that matters is Cost of repair as a percentage of the value of the vehicle. Period.
I really hope it all works out--it's a bad spot to be in all around.