I plan to move to another apartment next month to accommodate the awaited 2nd kitten with a dedicated playground room which will be shared by the two cats. I know about the basics of catification like litter boxes, eating bowls... etc. but what about the cat furniture distributed in the house highlighted below:
1) should I have the two tree mansions in the same room (living room), or different rooms?
2) should I have the window hammock in the same room (kitchen), or different rooms?
3) is it ok to have the two cat beds in the same room (bedroom), or different rooms?
4) do they share the "One Fast Cat" Wheel? Or do I need to buy two? If two, do I need to have them in two separate rooms?
5) the "Unconventional Cat Furniture" Boxes and Climbers, would one FULL set of each be enough for two cats? Or do I need to buy two from each?
6) is there anything else I should consider that I may have forgotten?

As per the breeder of the second kitten, her cats love cuddle/sleep/share together any piece of cat furniture. And she has pictures of them sleeping over each other on one tree mansion, and leaving the other tree mansions empty in the same room. So she thinks having their furniture in the same room is fine.

Thank you in advance.

PS I'm not addressing here the stud isolation room for I know the set up for that... if and only if, I decide to proceed with breeding them.

I can only speak for my two boys, but they share everything except for their food bowls. 2 litter trays side by side and 2 cat trees side by side in the sun room. Both of the trees are large enough for them to be on at the same time and they take turns at who gets the highest spot.
They share the same toys and are generally within sight of each other most of the time. They don't have actual cat beds, but avail themselves of our bed, or either of the 2 other spare beds in the house at night, depending on their mood.

Your entire home needs to be catified! Not just their room. Whatever you have space for. Definitely a cat tree in their room and at least one other one in the living area. If you can spare one in the bedroom (if they are going to be in there), do it. If you don't want to do a cat tree, get some milk crates and stack them in step form. I'm sure you won't be able to add shelving to the walls. Have cat beds everywhere, although cats tend to sleep where they want. You will only want ONE feeding area for the both of them. Litter box placement is very important -- two cats -- three boxes. They make fabulous furniture that will "hide" the box. One cat wheel will be plenty. They will not be on it 24/7 anyway. And, just like human siblings, cats need to learn to share.

So, put up all the hammocks you want, place cat trees or climbing things everywhere. Lots of scratching posts. Plenty of beds. You will be a mad cat man when people come to visit! Naturally, you can always start out small and add things as you go or as you see the need for them.

Have a safe move.

Catify all over the house, do not restrict it to the cat room. When Echo and Ishka arrived, they had their room and several spaces, but after a while they started, seemingly, to compete for space. The behaviourist told us off because whe had not catified every single room of the house... now we live in a little corner and all the rooms are theirs :-)
Nah, really, add cat trees, cat scratchers and cat resources everywhere you can. Above all if you are going to have two.

Iria