I know some (most?) of the non-essential electronic stuff and probably the air conditioner will never work if I get one, I'm not too bothered by that. I have read that you have to pull the windshield to remove the dash and a W140 is too big to fit in my garage, so yeah not happening.

Of the issues with this particular one, the main stuff I am not sure about are the battery drain and all the gauges not working (it seems like most of them have this problem though).

Ideally if I get one I could make it reliable enough to get in and drive 400 miles if I wanted, and (with an OM606 swap) have enough power to be in the ~9 second 0-60 range so I could merge onto the freeway without having to worry too much. I have driven a couple stock ones and I know they are way slower than that, but I have daily driven a W126 300SD and 300SDL so I am used to it.