Numerous buses from all around Bulgaria arrive at summertime.
Make sure to visit the old town. Nearby campings all around the city are also popular for young people and backpackers.
For a lesser known place to go and relax, there is a rocky area by the sea in the old town. Walk up past the old school (apparently an old school anyway) and over the car park and follow a little path down to the sea. There you can sunbathe on the rocks, swim in the sea or jump/dive off the rocks (some are quite high!) if you are feeling a little more adventurous. The sea is quite deep here and can be a little rough at times so make sure you take this into consideration if you are not a fairly strong swimmer.
Buying real estate in Sozopol should be a good deal. It is very nice and beautiful place, not yet discovered so much by tourists and not crowded.
A good way to find a place to stay is to ask a taxi driver to take you to a place they know. This usually involves them taking you to a property they own or one owned by a family member or friend. The best place to stay is the old town where you will feel in the heart of the cultural side of Sozopol. The people are friendly and welcoming and it is not far to walk to the main part of the town for food, drink and to visit the shops.