No you don't have to install the G3 BG2 Fixpack, you can, but it's not required (by the basic principle of the program)... as only the BiG World tools are required, which are not actually game content adding mods.
Jarno, why are you spreading misinformation like this to newcomers? Do you seriously not know better? It is very bad for the project. The fixpack, in fact, *must* be installed to ensure proper functioning of all mods in the BWP.
Well, I do know better... yes, some of the mods might require the G3 Fixpack, but most of those mention it in the readme ... or they are badly coded. Yes, the mods can add the exact same functions as the Fixpack if they are required and if you don't do that, you are a bad coder as is. That's my line, yours might be way out there elsewhere. Yes, and I know I too am a bad coder, as one of my mods won't install on the vanilla BG2 game without the help of the BG2 Fixpack... but I never contest it ! Unlike say you, a guest without a reply address. 
If you look for example the Rogue Rebalancing, it shouldn't require the G3 mod, it works with and without it, as there's a redundancy code just for this case, and it needs to always be installed after the G3 Fixpack... but normally you won't notice it as you don't need to. Well unless you wish to make a special installation where every decision matters. There is examples, like installing the formally waring mods... the G3 and the Baldurdash -_Fixpacks.... the BWP has traditionally made the definite decision to op out the latter while making the consequent mods compatible with fixes etc things. This was later amended with more fixes, but the mod still doesn't install all major component tweaks as it could without the BWP's influence(as in vanilla mod).
BUT those traditions are not all healthy. I would say that insisting the BGTMusic to be installed after the BGT is baseless, and it can cause harm too, and were it the version that came out with v1.05b, the requirement would be fixed already, as it would remove songs for major mods that are installed before it. AKA this:
when I install the full BG/SoA/ToB music component some of the music wont play and at least one place uses wrong music track.
But there's other aspect too, the fact that the BGT would then require the ToBEx ... shall we make a quote castle ? (of the things that are bad with this approach)
And if the current BWS doesn't allow the BGT to be installed without the BGTMusic... then it's a problem in the current BWS, as it did allow that in the previous versions.
Edited by The Imp, 15 November 2013 - 12:30 PM.
Yep, Jarno Mikkola. my Mega Mod FAQ. Use of the BWS, and how to use it(scroll down that post a bit).
OK, desert dweller, welcome to the sanity, you are free to search for the limit, it's out there, we drew it in the sand. Ouh, actually it was still snow then.. but anyways.
