Thanks much for your detailed response.
I have power assisted doors and trunk, but no power trunk closer....no red button. Holding the headrest button doesn't help. The parking brake pedal is attached, but the plastic release handle on the dash has been detached from the cable. With the temp sensor, I'm worried it could be some other problem since the display sometimes shows nothing.
The sensor sometimes reading nothing and sometimes reading 140 argues the sensor is bad or there is a short in the wiring. I'll bet on the sensor. It should be a cheap fix. It's almost certainly not the display which would be much more complicated. I could be wrong, but I'd start at the sensor end of the chain.
I'm a little stumped with the trunk problem. You have an automatic trunk release, but it doesn't open the trunk full open and there is no power assist to close the trunk? Maybe it's a model year issue; my '04 has soft-close doors and power trunk opening and closing assist as part of a single option. So the trunk latches okay and unlatches remotely, but it's hard to close by hand? Don't know why it would be difficult to close by hand unless you are pushing against the hydraulics that open and close it.
The headrests are also a mystery. Their release isn't hydraulic, it's an electrical switch, I think. Could be a fuse. Shouldn't be overly complicated to figure out and fix.
The parking brake release may be as simple as reattaching it. It may involve replacing a part or two and one end of the cable or the other, but it should be straightforward. It's a mechanical piece; no hydraulics or pneumatics involved.
I'd find an indie shop that specializes in MRZ cars. Shouldn't be hard in your area. Let them trouble-shoot the problems. I really don't think they are going to be expensive fixes. None of those problems are likely symptoms of some sort of massive electronic systems collapse. A couple of hundred bucks and you're back in perfect shape.
I see you have a Silver Arrow as well. The R129 forum on this site is very friendly and very savvy about the R129 chassis. People will want to steal your SA, but you'll get lots of good advice from them.
Did you take my advice and check in with the W220 forum? They may have a $10/5 minute fix on the tips of their fingers. I would check there rather than this forum anyway; the W220 is not common enough that readers of this general forum would necessarily be able to help. It is also the flagship car, so it usually gets new electronics and drivetrain changes first so people will smaller versions may not be familiar with the new stuff.