OP, I can see that you love him and his traits apart from the hoarding.
But he needs to face up to this and deal with it, clear his house, rent it out, or he stays there on his own and doesn't move in. As I said in my earlier post, he cannot bring this into your life.
He does have a mental health issue, and the only way forward for him is to accet that and get some counselling and help to clear his house.
He needs definitive lists:
Does it work?
What do I need it for? and define a use
Find a home for it
If its a precious memory, put it in the memory box
Clothes - when did I last wear it, are there any holes etc
Shoes - as above
He needs to stick to this. Nobody needs 5 kettles, 6 toasters, broken shoes/whatever, and he needs to get past the mental block that is making him keep falling apart shoes, that nobody in their right mind would keep.
Find safe storage for the things that do really have to be kept, like stacking Really Useful boxes etc, or racking .
Any genuine collections, either go on display or get boxed safely in secure sealed tubs until they can be displayed. I used to collect mugs and special candles, my brother used to collect model cars. People can collect stuff without hoarding it.