Always get two kittens to begin with. They may hate each other as they mature, but with litter siblings it’s usually ok (conversely, never ever get litter sibling puppies).
They will always be the wrong side of any closed door and will yowl, or scratch the carpet/door frame, or both. When they’re tiny they’ll use the entire house as a theme park. They’ll stop shimming up the curtains to cling onto the curtain rail, soon after it’s fallen down with them attached to it, and embarrassed them. They’ll experiment with plant it’s as alternative litter trays. They’ll nibble indoor plants, some (eg spider plants) they’ll just sick up, some (eg lilies) are dangerously toxic.
They may really, really love their tummies being stroked. They may really, really hate it when they’re a bit older, and let you know with teeth and claws. Little children especially don’t enjoy the cat drawing blood on them.
They may love watching birds from the windowsill. They may prefer bringing a live bird in, to chase around while it sheds feathers and poo all over the house. They may just kill it and leave the corpse under a bed, unnoticed until you smell it.
Dark cats will mostly choose your whitest clothes or towels as a bed. White cats will prefer your darkest clothes. Especially freshly washed and folded.
They’ll love a particular food for weeks and weeks, then when you’ve stocked up with three months’ worth, they’ll go right off it. Then they may tell all the neighbours that you’re starving them.
I’ve had only one of my 60+ years without a cat or two (or 3, 4, 5…). I hope you enjoy yours. Photos when it happens!