Here's my advice based on my recent purchase.
Get an 05+ facelift model. Looks better and most issues with the pre-facelift model are sorted.
Hold out for the spec you want. An E65 with no options is a waste of time.
You want a sport model (standard dynamic drive) or an SE with Dynamic Drive. This is essentially active ARBs and make the car sit absolutely flat in corners. It's a sporty drive so you might as well have it handle properly too.
Comfort seats are a must have.
Bluetooth with telematics is a must have.
Soft close doors are awesome.
Auto bootlid is also awesome and I highly recommend it.
Comfort access (keyless) is nice but I don't miss having it.
EDC is very nice but not neccessary.
Logic 7 audio is good but the stock hifi isn't terrible once set up properly.
Heads up display, night vision, adaptive lights, adaptive cruise are all cool but you won't use them much so don't pay extra for them.
Servicing is based on BMW's conditional servicing scheme so you don't end up servicing things that don't need it. Concequentially, it's not expensive to maintain.
Performance is good for all models except the 3.0 petrol which, although acceptable, needs to be thrashed to maintain good progress.
4.0 V8 740i is pointless as it's costs the same to buy and run as 5.0 V8 750i.
Avoid the 6.0 V12 760i unless you are totally minted, in which case you won't be looking at an E65 anyway.
Nav is standard as is a fair few other items. Higher the model, the more standard kit.
The interior layout takes a bit of getting used to (column shifter, one touch stalks, push-button parking brake) but feels very natural once learned.
Don't belive what anyone says about iDrive. It's a piece of cake to use and will take 5 seconds to learn.
No major weak point to speak of other than the usual electrical gremlins when the battery get towards it's end of life.