Not much of a write up, more of a rambling with links to some good information.
You can leave the inlet in place no problem, I took mine off to do the valley pan and it also helped with the PCV.
That's young for headgaskets, I can only think it was seriously overheated or misdiagnosed and you will probably find your guides are fine and the chains are like new at 78K but if you plan on keeping it and have the cash then why not.
I think it is quite rare for the guides to go and trash the engine as I think it normally just makes a lot of noise and as long as it isn't driven I think most are ok but there are a few cylinder heads on eBay with damaged valves ....

I think it was a matter of wealthy owner and a take advantage garage
The parts bill was massive
6 months ago they charged them £650 for a front strut with bag That was just the part. Labour extra !

I would imagine the head gasket bill was £4K +, they probably didn't change anything !

Hope they did as i can see a lot of new nuts !