Do I have to take all the fluids out of my Mustang, to store?

A car needs to be driven periodically or it develops big problems. Or you have to go through a rather elaborate draining and preserving process to "mothball" it, with no guarantees that big problems won't develop anyway - better that it gets driven.

Do you have any relatives that need a new car desperately, but when they're dumping money into their old car to keep it running they don't have the money to buy something nice? Or an older relative that doesn't drive much but needs a car for errands?

Make a long-term loan of your car, all they have to do is maintain and insure it properly and not wrap it around a tree. (Or you can pay part of the insurance, depends on the situation.) And they can save their pennies for a new car when you get back from wherever.

I like finding Win-Win solutions when possible. ;-)

But set up some terms, and put it in writing like a lease with the payments deferred as long as they follow the terms - they might get the idea that it's "theirs" and sell it.

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change the oil ... fill the tank ... remove the battery... start car run every few months to operating temp