Don't forget all the housing items.

I got a private medium house, a FC room and a Flat so for all the indoor items it's not really a problem, i can stock in my room or my flat. Moreover there will increase it in SB (only for houses ?). But people with nothing, or just a flat or a room and who are waiting for a FC/private house, all these items (events, retainers missions) accumulate in inventory/retainer.

For garden furnitures, there is a limitation and no increase expected in SB. I got a retainer with many garden items : I can't sell them because already used, and one day I could change my garden. They are expensive (trials special items for example), so it would be a waste to trash them.