That is so considerate thank you!! You've made my week ^^
The solution would be more variants of partitions that is longer and the lieks and maybe with dual layers where you can dual color them or so... anyhow the challenge IS with housing... and the real challenge IS to use all floors in the house with the given amount of item spaces we got now... many end with locking off areas, which makes it question one, why chose medium and large to begin with?
I think the numbers the OP posted may be a bit too high, here are my more modest slot expansion ideas.
Apartments/FC rooms: 150
Cottages: 25 outside, 250 inside
Houses: 40 outside, 400 inside
Mansions: 60 outside, 600 inside
Mansions should get the largest expansion if they had to choose one size for slot expansion since 400 is way too small for how large they are. I actually would like to fill up the entire space of all floors without it looking barren.
I just want the f****ng ability to change the interior and ceiling and remove the godawful pillars. Most of the slots go to hiding them.