Right off the bat, I wouldn't buy the powder, the brass, or the manuals(unless they are fairly recently published). You don't know how many times the brass has been reloaded, and you don't know how old the powder is, how it has been stored, or if a powder happened to be poured back into the wrong container, and there is plenty of reloading data and information available for free on the internet.
Second. Is the Dillon press completely converted to a 550? You can upgrade a 450 to a 550 without the benefit of the quick change toolheads. In other words, while it may have the primer and other components, the main frame may not have been converted. Which leads to the next question. Are all the conversion kits for the Dillon?
To be real honest with you, that sounds a bit steep for what you are getting. Not to say with 100% certainty it isn't worth it. But one would need quite a bit more information and spend a good hour or so determining if it is truly a deal.
Is the scale accurate?
Are the presses worn out?
Are the dies scratched or otherwise worn out?
Do you REALLY need, and/or are you really capable of offloading the stuff you don't want?
Are the bullets really commercially made?