Hello and welcome to your new adventure!
An adventure pack is an optional download you can buy that has dungeons, monsters, and loot. IT tyically has it's own story-line and series of quests. You can make purchases for them at the SOE Station website. Splitpaw Saga is definately worth looking into.
Your Station Players pack gives you the EQ2Players extra functions, and allows you access to any of SOE's games. Planetside, Dark Age of Camelot, EQ1, etc. You of course will need to purchase the initial software, but you can go and play those games with your pass, no extra charge.
There are many servers to choose from, you make your selection during chracter creation. Najena is a good one with lots of guilds of all level ranges, and many players in the zones. There's never any difficulty in finding a group.
You will have (I believe) 8 character slots. They can all be on the same server or you can assign them to different servers. Remember, you cannot transfer money and loot between servers.
As far as the game goes, it is like any other MMORPG - you adventure, quest, fight, win, die. You will enjoy the graphics of the game, and find the economy much easier to work with than your previous game.
There is a lot of solo and group content, plus thousands of quests to be done. You will always have something to do.
If you pick Najena, look me up. I can help you get started. :)