*hug* Calm down, dear.
I've had now probably 2 dozen cats desexed in the last 10 years or so.
It's not a big deal anymore, truly.
Your beautiful little Mikka will be okay.
Answers to your questions vary with each kitty, but basically, you treat her as normal, just don't "play rough" with her or pick her up *too* much. If you *do* pick her up, you get one hand under her rear feet and one hand under her chest to support her without putting too much pressure on her surgical area.
Personally, I've never had any of my cats (and I'm only speaking of the females who were spayed at the moment as it's different from desexing a male) have any adverse affects.
They are a bit groggy, a little wobbly, but otherwise, they are fine.
The vet will tell you, probably, to replace the litter in the litter box with shredded newspaper for a few days to prevent foreign particles from getting on the incision area. So yes, she can pee and poo.
She'll need a little water at first, then within about 8 hours, a little food.
I'd also suggest you confine her to a small area (one room - her favorite, or a bathroom) for the first day or so just so she will be encouraged to be calmer. But I've had cats inside and out go right back to life as usual.
I'd not leave her alone the first day home if at all possible *just* as a precaution, but if you confine her, even that's possible.
Daily, check the stitches area to see if they look red or "puffy". It is unlikely they will, but that's a sign of infection and early detection will keep her safe. She *may* lick at the stitches, but she may not. It depends on the kitty. If she does, try to discourage it *too* much, especially if the licking looks like she's biting or pulling on the stitches. If *that* happens, she may have to have one of those Elizabethan collar things - which she will hate, LOL!
And she should be completely "back to normal" in about a week. Although, personally, I was still careful picking any of the girls up for at least a month, LOL! But that's just me.