Glad you got brooder set up help from Shezbug and Mockinbirdiva and you have the little one on his own now
Both the problems you posted, the excessive amount of air in the crop, and the over feeding are both caused by your hens feeding technique. Firstly feeding too little with the little one continuously gulping nothing, then by over feeding. That actually happened to me once, she over fed the little one so much I honestly thought they were going to pop! It went down and luckily my girl didn´t do that to him again.
Overfeeding the little ones can cause the crop to stretch.
Do you have some formula on hand? I would definitely have it ready, just in case.
Allow the hen to feed him, as said above, but if you notice she is not, or is ¨feeding air¨ again, then stop her, and feed the little one yourself, preparing the formula as per package instructions (look at those closely as for the first week the consistency changes daily). You can get a feeding response from the chick by gently touching their beak (I put my thumb and first finger together, so my nails mimick a beak, and super gently touch the beak).
Definitely get yourself a critter carrier. It´s easier to clean, easier to monitor the chick etc you can position the thermometer and hygrometer so you can read them through the container without opening it.
Also, lots of bedding - as the chick gets older you will need to change it more often.
A thermometer (if you don´t have one already) for checking food temp