I don't think you'll have to get too carried away. Changing fluids will be a good idea, but after you drive it just a few miles.
If it were mine, I'd try to get some fresh gas in it, then drain the oil and put in a new filter. I'd start it up and drive it about 20 miles to get it to operating temperature, then drain the oil and change the filter. Another oil change in about 500 or 1,000 miles wouldn't hurt, then go onto a good frequent oil change program.
Things to change for sure would be; flush and bleed brakes, transmission fluid and filter, air filter( it wouldn't hurt to ensure that the intake tract leading to the filter doesn't have any critter nests before starting)
Give a very close look at belts and hoses.
Sounds like a really fun project, if I were there I'd get a kick out of helping.
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in