Answer to "incredibly low volume and a ton of sound leakage"With very low volume, I fixed mine by using isopropyl alcohol and a qtip/ear bud. Gave it a good deep clean and restored sound perfectly for me.
Answer to "change broken lcd with lost apple watch lcd"Yes. You can replace your cracked screen from an iCloud Locked unit. Apple does not ban any devices.
Answer to "Can iPhone SE logic boards be swapped to access data?"Technically, yes. But if the liquid damage is to severe the motherboard may not work at all.