There are potentially many unknowns and unknowns unknowns.
My suggestion is to create a plan for the migration / update, test a small sample data set, document (in great detail) what you actually do, then execute.
I would first create a backup, that is verified, of the current systems (Oracle especially) before doing ANYTHING.
and yes I did bold / caps / underlining / red font on purpose
I would also make sure that you have the new Oracle 19c EGDB shell ready for the data and enabled as an Enterprise Geodatabase so you can minimize any potential downtime.
Hope all this info help, good luck, and happy migration!
--- George T.