It isn't necessary to kill the Shadow Dragon. As long as you have the Wardstone in your inventory and you don't try to talk to him, he will completely ignore you. An 11th Level Sorcerer should think twice about getting into such an unnecessary fight. But if you believe in righteousness and you want to be a hero, then why would you allow such a monster to live?
Fighting the Shadow Dragon at 11th Level is probably about as hard as fighting a tanar'ri at 8th Level. (Yes, doing the Planar Sphere quest at 8th Level is a very humbling experience. I know, because I tried it myself.)
But if you use the right tactics, I give you a 33% chance of success.
Here are a few tips.
The Shadow Dragon's breath weapon can cause level drain. This will cause spellcasters to lose memorized spells, which is very inconvenient. You can prevent being level-drained by using the Priest spell called Negative Plane Protection. I can't remember whether a scroll of Protection from Undead also prevents level drain. Any dragon's breath weapon also does enough damage to kill characters who have a low number of hit points. Some of the dragon's other attacks, such as the wing buffet, are also a lot of fun to deal with.
You can avoid some of his attacks by hiding behind the columns on the east side of the room where he can't reach you. (That's known as using the terrain to your advantage.) If you try to use summoned creatures as "cannon fodder", he will probably dispel them with a Death spell if you have Throne of Bhaal installed.
Dragons are spellcasters, and they can buff themselves up. If you're not familiar with spells like Stoneskin and their counterparts like Breach, look them up in your manual. Since you're playing a Sorcerer, you want to know as much as you can about those kinds of spells, anyway.
Dragons, like many other monsters, have magic resistance. The Wizard spell called Lower Resistance and the Priest Spell called Magic Resistance can lower their magic resistance. (I don't think that was the original intention of the Priest spell Magic Resistance, but that's how it works in practice.)
Hitting a dragon really hard when he isn't protected by any protection spells can kill him, but it might take a while. You can expect a tough fight.
By the way, the order in which you do the major quests can make a difference. Some quests are easier than others, and I think it's better to do the easiest ones first. After the Circus Quest (which doesn't yield a huge monetary reward), Nalia's Keep is probably the best one to do first. (If you meet Nalia in the Copper Coronet, she will ask you to defend her family's home against invaders.) When you return to Athkatla, you might want to look into the injustices that are taking place at the Copper Coronet (start your investigation peacefully so that you'll have complete access). Then there's Korgan's quest, if that interests you. Certain cues will lead you to the Graveyard District, and you can get some gold and experience from plundering the tombs there if that's your cup of tea. (There are monsters and treasure there...what else do you need to know?)
If you talk to people and pay attention to what's going on, you'll end up on several easy quests. I emphasize that it's a good idea to pay attention to what people in town are talking about. For example, if you hear about a really good play that's being performed, then you really ought to go see it, right?
I wouldn't walk inside every house in town (BG2 is a little different from BG1 in that respect), but sometimes there's an advantage in doing so. Usually, when you visit an area you've never been to before, an NPC will walk up to you and give you a cue. NPCs in your party will also give you cues.
A couple of years ago, someone here was complaining that a certain stronghold quest should have come with a "warning label". Even though it's a stronghold quest, it is definitely not the first quest you should undertake. Or perhaps I should say,
because it
is a stronghold quest, you ought to undertake a few smaller quests first. If you're not prepared for it, you can
really get stuck. As an analogy, imagine being trapped inside a locked room and a monster who can only be hit with +3 weapons has the key, and you don't have a +3 weapon. My own reply at the time was that you should consider the stakes: if you need to raise 20,000 gold pieces and someone suggests a quest that could raise that amount, does it not stand to reason that such a lucrative reward might entail a bit of...danger? In my way of thinking, the higher the reward, the higher the risk. Before undertaking such a risky adventure, you ought to embark on smaller, less rewarding quests to prepare yourself for the really big, dangerous ones. But I suppose not everyone is used to thinking that way.
In any case, it goes to show that even though, as I said above, you should listen to what people say, you also need to use your own good judgment.