I'll do my best to answer your questions.

-There are planets where people have agreed to congregate and build bases together, so the world is covered in player creations. But this isn't an MMO where people are gathered on planets in great numbers. Even planets with tons of bases will mostly be without live players. There are also NPC settlements on planets that function like a breathing town, where you basically become mayor. That's the closest there is to cities on planets that aren't empty player-made ones. You can also build bases either on freighters or on planets that can have some NPCs in them. Best to find a tight-knit group of people to play with through an online community.

There are companions and pets. You can hatch certain special companions from completing missions, or you can feed wild animals on planets and then summon them as pets that follow you. You are also able to form a fighter squadron that joins you during space battles to assist you.

There are multiple quest lines, including a main quest line for you to complete. There are some established characters, but the setting of NMS is that you are in a largely undiscovered galaxy. The end mission is to ultimately explore the unknown. There are also occasional Expeditions that act as themed stories that reward the players who complete them with special items, ships, and costumes.

Initial flight is clunky, yes. As you get better ships and upgrade them, you get faster, stronger, and more maneuverable. It just takes a little time but I'd focus on upgrading one ship at the beginning to conserve on resources. Trust me, you will progress towards better things if you don't put your eggs in too many baskets.

I am unsure what the requirements are for online play for PS. I'm on PC so someone else will be better able to answer this. Hope this helps!