AndyBuzz: Apparently you are missing a file that is needed.Maybe WeiDU.exe.

For detailed instructions go to this page, it covers seemingly every question.

The basic guidelines are:
-Install BG1 and BG2, not in the default folder (C:\Program Files) to avoid UAC issues.

-Download the following files and extract/copy them in the BG2 folder:
a)BiG World Installpack
b)BiG World Trimpack
c)BiG World Fixpack
d)WeiDU.exe
e)BG2 fixpack
f)Restored Textscreen Music & English language pack
g)BGT

-Then run the batch file.

Another approach is to download the BiG World Setup (BWS), install it (again not in Program Files) or just extract it wherever you want (the exe is a self extracting archive) and run the BiG World Setup.vbs to have a nice GUI to choose all the mods and their options. But if you go for a "simple" BGT I don't think you need it.

As for recommended mods, there are plenty but many change the original experience in a very substantial way for newcomers to be really recommended. Either by altering difficulty, or simply by being amateur in quality etc. The usual advice is to get to know the game first and decide what would suit you better then.

Personally I would recommend you to take a look at BG2Tweaks to install a few ease-of-use components to make your life easier, such as infinite stacks on potions and ammo. Better limit yourself to those, in my opinion, and don't get temped to install others unless you know what they mean and how they affect gameplay.

Mekonis: For a person who's played through the entire Baldur's Gate series several times, can you suggest a good BigWorld setup for me? Specifically, can you name big content mods that work well with others? I don't want the MASSIVE HUGE EVERY MOD install, but I'd like one that adds a lot, without breaking the game, or adding senseless stuff just to add it.

AndyBuzz: Sorry, I can't help you on that. All the big mods change the game too drastically for my taste and I avoid them. And of what I've seen the quality is not proportional to their size.
But I'm quite critical to new content so maybe I'm not the best candidate for suggestions. I usually install tactical mods and few small(er?) content adventures depending on the mood.

The only thing I could tell you though is that with BWP you generally don't have to worry about what mods work well with others, especially if you go with one of their standard setups.

Sorry I couldn't be more helpful.