Much to talk about. I suspect you have done some research already besides looking at pics?
IF not, first do the following from the TABS above: BLOG --> Buyer's Guided [under categories] --> Scroll down to Ferrari 456 GT/GTA Buyer's Guide and download the guide.
or just click on this link: Ferrari 456 GT/GTA Buyer's Guide - Ferrari Life
Be glad to give as much as I can when the questions get 'narrower'.
BUT as a general rule of thumb If I were in the market again for that model:
- get the M series unless you are very very overly in love with the looks of the older GT
- buy only the best example you can find and after a good PPI on the usual suspects [I'll elaborate later]
- Do not be daunted by high mileage cars in the 456, 550 or 575 series
- A higher mileage car may be a much better car than a too low mileage car
PS: Since the Ms are less older than mine, but seemingly now starting to show signs of 'issues' lately, like CATs, Exhaust manifolds, shrinkage, and even window issues, I've been told, I would also look at the coolant system for excessive wear/corrosion and the leveling/shock areas for needed repair.
I'll let those that own them comment further. A well cared for M would be very little in expense to keep, like about $500/year I'm thinking but I'd budget about $1,500/year for a buffer.