Heee!
first of all, welcome to the community!
1. buying the 51 euro’s pack gives you the possibility to use World Builder to build your own worlds. Althought they will not be used in Oort Online, unless there will come a feature where you can build your own worlds and set up a server with those worlds (but that is something to look forward to in the future). Besides that you will receive the title ‘Adventurer’ instead of ‘Explorer’ on the forum. Also you gain acces to special wearable items wich you do not have with the normal pack (31 euro’s). your name in the credits and you will receive the original soundtrack of Oort Online with the release next year. See for a list the main page ‘Oortonline.com’ and klick at ‘Get Acces’. Explorer = 31 euro’s steam pack. Adventurer = 51 euro’s steam pack (DLC thingie).
2. There are a lot of servers, it is all multiplayer but there aren’t that much players yet. I found a lot of activity atm in ‘Civini’ (central EU server, most activity is around the evening +1GMT). And yes, you can play with friends, it aren’t private servers.
Greetings