It sucks that you have to get very close to c to have much effect on perceived travel time. Like at 0.5 c, you only save about 15% of perceived travel time which is SOMETHING but not a project for the record books. It only gets significant at 0.99c or so. At that velocity, a trip of 100 light years would take you inside the ship a perceived time of about 14 years, still quite a long time to have to eat and such.
So 28 or 30 years passes by on ship time to make a round trip but still 200 years pass by on Earth, you arrive in a way different time than when you left and there would be nobody alive you knew at home. And you would STILL be 30 years older.
To make that say one year, you have to go something like 0.99999 c
So our first interstellar journey would have to be Alpha Centauri and at least that is three stars for one trip. At 0.5 c the total trip time would be not much different for the traveller and earth bound time flows. Maybe a year faster for the traveler than the time flow on Earth.
At least you would come back to a civilization not THAT much different, about 8 years compared to the example of traveling 100 light years at .99 c of about 200 years going by on Earth and 30 years for the travellers.