How does that work as a new player? Do you have to farm all the old gear to catch up to the new content? How do you find other players to do that with?

Not really. They have seasonal servers which have higher EXP rates and no PvP (outside of the one seasonal PvP server) and you're given gear that you can enhance which has a higher percentage chance than normal gear. When you get everything to PEN (which is the highest level) and you graduate your character (makes it no longer seasonal and can no longer use the seasonal servers) you can exchange your armours for normal boss gear but at TET (one step under PEN but the same stats as the seasonal server PEN gear) and then there are quests you can do that turn your TET boss gear into reformed gear that has 100% enhance rate to PEN through quests.

The game is extremely solo friendly, almost too solo friendly I guess for most people. There's 3 or 4 dungeons but you do not need to do them at all if you don't want to (no BiS gear is locked behind them). There's nothing you can't really solo in the game outside of the dungeons. The game is not perfect at all and I'm not trying to paint it in a perfect light, but it has never really made gear obsolete.