sudocrem is also acceptable for sore kitty bums- Vet said just a little tho so it can be absorbed and not licked off. Just incase you have some in, if not, vaseline is probably the better thing to buy as it barriers against the moisture better unless the skin is red and or inflammed/swollen looking (sudocrem is actively soothing)
Re chicken, id give him as much as hes willing to take for now but in little amounts and proper mothers milk substitute milk as soon as you can. When one of mine was on chicken only i roast/poached/microwaved (?) it in a little water and gave him the chicken chopped up in the water it cooked in to give him more fluid. Remember cooked chicken bones splinter easily so shouldnt be given to twix as it might cause him to choke. you might also be best, when his poos return to normal to slowly switchback to the diet youve chosen by mixing in other food with chicken. im not used to kittens so young so hopefully one of the rescue peeps will be along soon with more help.
just seen your reply- dont feel quilty about his improvised pen, its safe and warm and has everything he needs (assuming theres a litter tray?) which is the important thing. its luxurious compared to the streets. cats are masters of never being quite satisfied no matter how much you give them and wrapping their slaves around their paws. its generally advised to separate dogs and cats for an initial period in any case as its hard to be sure how everyone will react once your asleep
Twix looks gorgeous (popped onto other thread)
to purrs