Welcome!
Well don't let the shop charge you for springs first off, you don't have any on an airstream

. Your shocks may or may not be good, if your axles are original they most likely need replaced someday, but don't stress about it.
Regarding plumbing, fill all the tanks with water right up to the grey water coming up out of your shower drain. Leave it overnight and look for leaks underneath later the next day. Check the operation of each flush valve. Check the freshwater tank for leaks, including leaks at the fill port. Check the water pump and all connections to it. Check the pump inlet filter for debris. Check under all cabinets.
Check the roof seals of your vent piping, they are rubber and only last 5 years or so. Failure is a common source of leaks.
I am sure I missed a few plumbing related items.... It's a start
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76 'Airstream Tradewind