you can do expo build:android --no-publish so it will just use the most recently published version, or use a different release channel for each platform but that will require uploading a new binary to switch the channels - read more about channels here
Yes, assuming you have configured OTA updates to work. --no-publish just means to use the last version of the code you published (which might be different than the current state of your project) for your build.
If you want to release to each platform independently, you’ll want to move to using different release channels by platform.