You're much more polite than meI get what you want to do, but Id suggest a vigorous de clutter and a few trips to the tip as a first step! Then you will be able to see what you need to do
As the owner of three sheds myself, with room under the house, in the greenhouse loft etc, there does come a time when you need to work out what you are doing. Preserving a few tonnes of junk for the future of the nation, or doing what you want to do with the cars, machines, etc you like.
Especially as time here limited, and you kids will simply skip the lot, paying for someone to do so, rather than hanging on to it "as it's worth xxx pounds . . . it was once, but now, after a decade of storage and the death of anyone who wanted it, it's just a waste of space, taking up the room to actually do something with some of the rest of the stuff.
So I've enjoyed sorting my cars and actually driving them - the feeling of satisfaction from simply unloading a load of stuff at the scrap man and getting paid for it, or over the side of a skip at the tip, or even giving it away to someone who might actually use it is pretty good.

