Hi Christophe!
Yes, by this point anyone who owns a Cougar is preserving it, even if they are running it daily.
How well you can preserve the paint will probably depend on where you store the car, how often you drive it, and in what conditions it is expected to live. Since she's probably 25 years old at this point, you must expect that she will show scars. I don't demand perfection, but if I did, only a full respray or coating will fix it.
The seats are another question of how often the car is used and - I hate to say this - the physique of the person driving it. One of my old cars (Tiger) was originally owned by a larger man, so the seat bolsters were pretty flat by the time I bought it. My current car (Florida) has apparently only been owned by smaller people like me, so the seats are perfect. I think that the best you can do is make sure that the leather/fabric is well cared for with cleaning and humectants. The underlying foam can be replaced, but it's not a fun job.
As for history, Unless your car has been serviced at a Ford garage, (or the same independent garage) for all of its life, you're probably out of luck unless the previous owner kept all receipts and gave them to you when you bought the car.
If you want my opinion... Service and clean her the best you can. Do your best for her as she is now, and don't worry too much about what happened before you knew her because you can't change it. You can fix things that you find, but don't panic about the past.