I don't know the 400 series well at all but many here do: Stay tuned. However, as a general rule I'd look at some service records if any, and look over general care of the soft parts, which is to say rubber and wires. Interior is not the big issue, but mechanics and seal and boots and someone that can work on a 12 cylinder Web. carb.
From the SN, that is an EARLY model so the Auto isn not an American mix IIRC and that means a few more bucks.
You NEED, a GOOD, PPI. It is not a guarantee, just a means to let you know what you are getting into and down the road. Personally I believe that engine is great, but and you mention you had cars, so thinking you could do the engine work, if needed on your own with PROPER REAL books.
However, even the champs on these things can sink a lot of time, effort and $$ into a museum piece. Very difficult to eval at this range. BUT, you'll get some standard, and honest and GOOD TO REMEMBER comments: Take them seriously and keep asking.
I know this isn't directly addressing 400s, but worthy of a read for older similar models http://www.ferrarilife.com/library/guides.php
PS: Prices can be as low as $15K-$50, but there is a LOT of diff between the two.
don't say where you are generally located so, assuming it's near the East, and going North.