Hi Cat,
Bless you for taking in this darling . First I would check the formula it is on . This could be causing the loose poop. Could be too rich.
Then I have noticed with new kits they need to get accustomed to your voice --so try and take time out of the day to just sit next to it and talk softly to it, if you can get a soft feather try using that to stroke it . This will allow it to get some sensory stimulation without being stressed by being directly touched or held. Most cats do not like to be held, they feel out of control. Eventually when trust is established it will be better.
Think like a mommy cat--she would not be holding her kit just licking , stimulating its little bum for defecation, allowing it to feed on her--so even when feeding try not holding the kit on its back. that is not the way they feed from mom and it makes them feel terribly vulnerable.
The stuffed animal is a great idea, and try and keep it wrapped lightly in a blanket as if it is with momma. Your voice will eventually be momma--it just takes a little time. You seem to be doing everything right.
Keep us posted on your baby. Good Luck, Cat