PVE
You can enable friendly fire but most people keep that off and you can only enable it for yourself... you can't force anyone into PVP... If the game was forced PVP I wouldn't play it at all. That is what keeps me from playing most survival type games.

You can play solo just fine. This is not an MMO and severs with people are typically limited in number of players. Players can steal stuff and ruin things... most people play with friends on password secured servers. Probably the majority of the playerbase plays solo though... IDK just guessing, but it seems that way.

It isn't overly difficult once you learn it... but you can die a lot learning the game. So a lot of people don't consider it heavy into the survival aspect. It is more looter where you find resources and craft them for better gear to move on to the next area where you farm resources etc. Base building for crafting and defense.

The different, random world seeds I find great for replay value... I enjoy the exploration and finding logistically good locations for resources for making bases etc. For me it isn't about completing a game to just kill bosses. Once I explore and build up the world for the final boss I start a new world seed. You can have as many characters and worlds going as you please. You can also use characters on any of the worlds, they are individual saves separate from the world saves.

There is a tutorial raven.. if you get the game be sure to read his hints.