Default ports are the ones shown on the UI of the launcher: 7777 and 27015
Regarding Steam Client, yes both Ark and Exiles use UE4, but the versions used are very different (I think it was 4.8 for Ark and 4.15 for Exiles), I’m not sure what the reasons are - I’m not actually a game coder - but if Steam is running when the server is started, the initialization sequence will popup a bazilion of error message boxes.
Having the steam client run after the server is started is fine.