Well like I said it depends on your oracle`s database structure(the logical structure - tables,tablespace and so on..) and on the migration tool that you will use. If the database are small maybe consider using oracle_fdw to the oracle`s tables for the deltas. I didnt search online but maybe there is a tool that can manage logical replication between oracle and postgresql and that might help you.
It is very depends on the structure of your database. Before starting try to know everything about your database - schemas, object types and so on.. Ora2pg is a great tool but sometimes isnt enough for all migrations. Check out oracle_fdw("dblink" to oracle database) and orafce (oracle internal functions for postgresql).