The Ossus region is opened on the planetary map.
Travelling there will not destroy any story progress.
Only thing is:
Dailies are only opened up by doing the story.
As for "sightseeing" and using it as RP ground:
The hub is a nice outer rim village.
With farms.
So might be good for some rp backgrounds if someone needs it.
Also I can recommend a tour through the jedi temple.
It is one of the nicest pieces on the planet.
Especially the Relic Chamber with the immense star card projection is a wonderful sight.
So if anyone wants to explore:
Go for it!
Does not need story and maybe there is some interesting rp location there for any DM's.

Greetings
Corv