Being a 535i owner (wagon) I may be a bit biased, but no regrets on engine choice. To me the N55 is a superb engine, typical of what has made BMW a bit special over the years, a decent I6 engine.
As to a loaded car, I've bought into that as well, I've got most of what your example has. It is a greater risk, but the option is a stripped out example, where is the driving pleasure in that? I run with an extended warranty, see that as part of the running costs and for peace of mind.
Have you test driven the car, (you say it is a clean example), try it and then make a decision.
BTW, mine is now into its fifth year, no intentions of selling it on, as I'm enjoying all the options, puts a big smile on the face every time I drive it.
HighlandPete