Hi Hannikat and
I'm really pleased you are asking all these questions before you get a cat.
What I would say about rescues: they are not in rescue because there is something wrong with them... the majority who are in rescues are there because of human failings and through no fault of their own. They are as much in need of a good home as a pedigree.
THe only difference in my opinion between a pedigree and a rescue moggy is looks and a known bloodline. (again my opinion), and of course you're buying a pedigree rather than offering a good donation to a rescue. We have some wonderful members here who breed wonderful bengals and NFCs, and even they will tell you that taking on a pedigree is as much a responsibility as a rescue cat.
If you are keen on kittens then why not get 2? They will keep each other company during the day and provided you leave lots of toys for them to play with you will find they will sort themselves out well.
You might however wish to consider a pair of older cats. Rescues often have cats that come from the same household who should not be separated. In fact, the most devestating circumstance is older cats, often a pair or three, come into rescue because their human has passed away or can no longer look after them due to age. They are unsettled, and all they want generally is a good home where they can curl up on a lap and get a cuddle. Separating cats from the same household especially if they are very bonded is heartbreaking.
You have so many circumstances.
As for funiture and cat posts, if you train them early that should not be a problem, however, cats are cats and accidents happen. If they are stressed or have not been socialised properly then they might react by doing things that we as humans find strange, like scratching carpets and furniture. As a cat person, I was a little hesitant myself with my leather furniture. It has scratches now (by accident) but if I freak out about it its my problem, not the cat's. If I was very worried about it it might have reconsidered having a cat.
You have to take the bad with the good and sometimes furniture is going to get marked, problems that are stress or illness relate will arise, but you have to take it in your stride and remember the cat is doing what is instinctive to let you know there is either a problem or that they made a mistake.
Cats are pretty resilient but should not be treated as if they DON'T have fragile bones. Most cats will be fine on the landing but of coruse do keep an eye out on high spots they can easily fall and injure themselves. I often still look at mine and wonder how she doesn't hurt herself with how she jumps from place to place.
As for kittens feeding, it depends on their age, I would encourage you if you are getting kittens to get them when they are 13 weeks old or older if you can, where they have been weaned properly from their mum. Sometimes you don't have the choice on the age, but you should question any one rescue or breeder (if you go the pedigree route) who wishes to let you have the kittens before at the earliest 8 weeks. Reputable breeders will only release kittens once they are 12 or 13 weeks old some later.
Its a great decision you are making, but a very responsible one. THey become part of your family and have to be treated like they are. I think you'll find on this forum everyone feels their cats are their families so you will fit in just fine.
Hope I've at least started to answer some of your questions.
Good luck!!