It's good that you have some progress.
Hard to say what exactly is going on. You are running IBM Java, right? Supposedly default encoding should be UTF-8 these days. At least it seems so:
https://www.ibm.com/docs/en/i/7.4?topic=jc-default-java-fileencoding-default-charset-changed-utf-8.
No idea what options your IntelliJ or application may be setting, but if default is not UTF-8 then I guess many other things could go wrong.
Mind that there are three places where you can check and/or set default encodings in Java:
* file.encoding: System.getProperty("file.encoding")
* java.nio.Charset: Charset.defaultCharset()
* InputStreamReader encoding: InputStreamReader.getEncoding()
You should check them all and maybe re-adjust if needed.
You may also want to look for the environment variable
JAVA_TOOL_OPTIONS as it could be overriding non-default settings.
With regard to failures in the database updates, as soon as you are ready please send the error messages you are getting and we can try to help you.