1) If you already opened the milk carton and not put in fridge it will spoil. So I think you can either buy those small packets that LO can finish in one go, that way you don't need to store in fridge. Or if you buy the big carton then just store in fridge. Drinking cold milk is totally fine unless your LO doesn't like it. My girl loves cold stuff, she even likes licking ice so no issue there 😛
2) I don't think you should let baby sleep in yaolan for the whole night since there are risk of falling or suffocation. I also recently weaned my girl off night latching, it's definitely very challenging. I tried to sleep in a different room and let my husband take care of it because if baby sees me it will be more difficult. So you need to rely on other caretakers (husband, mother, helper etc). Either offer a bottle or just try to calm baby down by other means like rocking, singing. It's very difficult, but once you succeeded for one night, the next night will become easier and easier. The first night for me was terrible as we all didn't get much sleep but the second night was already better and after 3-4 nights she's completely fine, and within 2 weeks she could finally sleep through the night. So it's difficult but it happens very fast as babies are super adaptable. Just give it a go and stick with it. Good luck!