I have flown with my cat in cargo. My advice is let them get use to the carrier. i used feliway spray in the carrier the night before and just before put her in the case.
This doesn't work for me because mine has a tantrum and rages for hours. i pin her down with her head in an arm lock and cut all claws. I am similar to the OP in that i started young.
have you tried Burrito instead of scuffing. Scuffing sends mine into a hiss rage.
Mine didn't like many food at that age. I continued to introduce new food to her regular. I would watch out for cat food sales and buy big for her to try.
I brought a bit of nearly every brand on the market.
In the end i found a food she loves. I would put the food down and leave it there...
Take the time to harness train all cats so they are comfortable wearing it. That way you can restrain them when needed.
I have flown with my cat and i feliway sprayed her carrier to reduce stress.
Try putting tin foil on item you don't want him to scratch. The house might look like a space ship for a month or two but they usually learn to not scratch anything but their scratchers.
Mine use to think her carrier was a safe spot and slept in it most nights - blanket, feliway inside etc. This stopped after a couple of visits to the vet and that ended.
When mine was a kitten, if she was noise at bed time she went to the bath room with toys and fun stuff , if she was quiet...
Go to Bunnings and buy either of these and put it over the carpet in the areas she is scratching. I used them in a rental to protect the carpet in the litter box area.
https://www.bunnings.com.au/ideal-dyi-67cm-herringbone-carpet-protector_p6611138...
Are you feeding her enough?
Kittens should eat as much as they want at that age. Remember she is growing and has crazy energy.
When mine was that age my vet said feed her as much as she will eat.
Have you tried having two boxes next to each other?
another thing to check is making sure she can bet into poo position in the box? Mine will go outside the box if her tail is hitting the wall behind the box. To over come this i place my boxes about 10cm from the wall.
You can buy the single packets they are usually on sale in Coles every couple of weeks.
Pet barn lets you return any food your cat doesn't like no questioned asked. On a sales weekend buy 2-3 of each type of food and try them. Mine might eat it the first time and leave it the second or never...