I can't answer all of your questions, but I can answer some of them, at least.
1.) There are no such things as Subjobs in EQ2. You have an Adventuring class, and a Crafting class. If you're a Shadowknight, you can't sub in Assassin. However, you're not restricted to just one character, so if you want to make an Assassin alt, you can do that. The limit is a total of six characters - that can be all on one server, or across several different servers, but no more than 6 total. If you get the All Access pass, that ups your limit to 10 characters.
2.) Any race can be any class. Dark Elves make fine Shadowknights - it's practically their signature class.
3.) Shadowknights are tanks. They're designed to stand and take a beating, not to dish it out. That's not to say that they can't dish out the damage, but that's not their main focus. I don't believe that SKs can dual wield - they're doing their job best with a 1-handed weapon in one hand, and a shield in the other.
4.) Shadowknights' main purpose in a group is to tank. However, they (like any other class) are capable of soloing - unlike FFXI, you can actually solo past level 15 in EQ2, and don't have to stand around looking for a group for hours.
5.) Yes, there are lots of quests. Thousands. You get a Quest Book that is restricted to having 75 (or so - my partner currently has 78 quests, for some reason) active quests at a time, and by the time you get to Lv. 30, you may very well have reached the limit.
6.) No, it's not that hard to make money in EQ2. No, you're not going to have to camp Heroic monsters for hours on end just to be able to afford the gear you need to do your job. In fact, player-crafted items are usually pretty affordable, and are usually the second-best equipment you can have at any point.
7.) I have no idea whether you'll have trouble getting the name Dalamar. If you can't get it on one server, try another. Unlike FFXI, you're not restricted on which servers you can create characters.