1) no, eventually you will be able to be killed whenever you are in the game
2) no, a single player will not be able to place a Totem, although they can now. A Homestead will be used instead. Baskets can be used to safegurad your items.
3) all player driven
4) yes, the game is an RPG, meaning a Role playing game. It is also a sandbox, meaning there are no preset roles. A solo player could just fish and drink water, and watch the game, if they wanted. I want to play the old crank that lives up that side canyon ....
Solo players can place a totem and create a 1-man tribe. The tribe area is a safe zone if they chose to be good/neutral, not safe for evil. This will change a bit by launch, solo players will get 'Homestead', its not announced yet how it will be different from a tribe, but I'm pretty sure it will be safe as well.
3. There are no NPC towns in the game. You can go to other tribe's area and trade with them. Tribes can set up quests as well at their totem for non-tribe players.
4. Absolutely. You will need to trade with others, will have to make friends and so on, but its not necessary to join a tribe. This is my opinion only of course.