I did a quick skim through the thread (mostly by ctrl+F every single page) and couldn't figure out how furniture works. I purchase some furnitures from the slum dealer, but when I use the item it just disappears. How I place them?
In your Guild Home there's a lady at the reception. She can change the layout of your apartment and tell you how many points you've collected for each style.
Using the item in your inventory adds to these points.
Each style comes with a different benefit:
Normal: Nothing (afaik)
Poor: increased item drop rate
Casual: Increased EXP for Konoha
Luxury: Increased Money
Citadel / Cathedral: Inreased DEF and Magic DEF
Erotic: Decreased ZP during fights (according to the MTL)