Possible Purchase, please help with some Q&A....

Eli- There is a ton of info on the 550, specs, driving and maintenance experience, particular or recurring problems, etc. that you can find here if you use the search function. This is not meant as a **** you, but instead of trying to recreate all the info, and there's alot of it, it's worth your taking the time to research the archives here using the search function.
In brief, I can tell you what i know:

I had 2 550's, a 97 berlinetta and a 2001 barchetta. As with many cars, the later models of a modern production car are often more desirable, not just because of the year of manufacture, or low mileage- which is not always a positive sign with Ferraris- but because there are often incremental improvements, not really designated by a model change, as such, that get built into the car.
There were a number of factory campaigns on the 550 over the years as well, including replacing the wheels, which could crack under stress, certain ECU and motor mount problems (not sure the latter was a recall as such, but i think Ferrari sorted the problem at their expense), coolant hose problems- cheap fix, but a pain in the ass if you blow the coolant hose under the plenum- it's labor to get to and no fun if you are out on the road when you loose your cool(ant), The rear window has a tendancy to delaminate, and the later cars had a carbon fibre inserts on the console and instrument binnacle which some find preferable to the more stark rubberized material used on the earlier cars.
None of this is meant to suggest that the car is problematic. While it has its detractors- folks who wish Ferrari had been more adventurous in introducing a successor to the mid-engined Testarossa series from the mid-80's, it follows the tried and true formula of the Daytona- front engined, rear wheel drive two seat GT. The car is big, heavy, luxurious, and moves quite quickly. It is fairly easy to maneuver, although it is not a boy-racer, more a continent masher, and will exhibit some body roll on hard cornering. I think there are mixed views on the Fiorano handling package, which may improve handling characteristics, but provide a harsher ride. The car is closer to a daily driver than any previous 12 cyl. Ferrari, and is generally regarded as the best of the modern production cars they have made.
They are pretty cheap- i don't know if they have fully bottomed in price, and you are getting a huge amount of car for the dough- i'd rather have a 550 than a 360 for equivalent money, but, again, there are significant differences in the kind of car it is. The only way to buy a ferrari, even a late model, is to either go thru an authorized dealer who knows the history of the car, can provide a warranty, etc. or get the car fully vetted by an independent expert. Sometimes the garage queens are more problematic because they have been sitting and the rubber is dried out (those coolant hoses should probably be replaced); keep in mind that a few thousand saved on the initial purchase price can be quickly lost in repair bills if the car has needs. These cars are not cheap to work on, compared to Porsche, and parts are priced dearly. There should be any number of 550's on the market- the model is long in the tooth and due to be replaced-(i don't count the 575 as a real replacement but an interim step), so you should be able to find color/interior and options as you want. Don't compromise, though- buy the best possible car you can afford- the incremental differences in price become meaningless if the cheap car has needs.
ON pricing, i'm thinking 130k dollars should buy a pretty good example, on average. Don't know the particulars of the car you have been offered- mileage, color, options, etc. You can spend several thousand dollars on periodic engine service (belt service), so, again, you need to know the service history of the car to assess what you are buying.