BG2's itemization alone requires hand-crafting, and coding unique effects for, tons and tons and tons of items
Handcrafting - yes, but I don't think it's too hard to implement in code. Most of BG's items effects were similar to existing spells (just spell on hit or permanent buffs on the user), others were +XdY of %type% damage or +X apr. They just felt really unique because they were designed that way. They had great descriptions, which fitted with their actual properties, and really felt like magic items in a fantasy world. Compare BG2 with titles that use diablo-like itemization. +3% fire res. +7.5% move speed +5ft javelin throwing range is not a proper Magic Item.
Yes, this. Our itemization is one of the least difficult things to implement for us. The most difficult part of creating unique items is making the 3D models, but that doesn't take a gargantuan effort either - it's much easier to do than creating new enemy models, for example, since it's just a model, no animation rigging and stuff.
Effort required for a unique BG2 style weapon = 45% 3D model, 45% coming up with a proper backstory and integrating it to the world, and 10% actual scripting implementation, if I had to give a rough estimate.
We got some pretty decent tools that let us script pretty much anything into an item. We can even have a Lilarcor-style sword that talks to you, and the bulk of the work would be to write all the dialogue. We also got a pretty good and efficient tool for writing dialogue trees (with a built-in testing functionality), so yeah.
In an hour of work, I can create between 3 and 5 unique items with their own backstory and interesting magical properties, and actually implementing them takes only a little bit of scripting depending on the item's effects. Like, say, I come up with a dagger that used to be wielded by a dreaded lich king and it paralyzes enemies on strike and does +1d4 damage against humanoids in addition to its 1d3 acid damage against all targets and its general +2 to hit and damage. All of these effects are easy to implement. If we were to take an entire weekend off to just create unique items, we'd end up with over two dozen of them or what. Probably more.
We're aware of the challenge and effort required to create a game as ambitious as this, and we're also aware of how much effort it takes/how difficult it is to implement each planned element of the game, so don't worry about that. Yes, of course, there's always the chance not every planned feature makes it into the initial release version, but if the game does well we're going to work on some expansions right away, so there's always a chance to see it later - and, most importantly, we've got a tight vision and know what we want from the game, so there won't be any terrible development decisions that fuck everything up like there was in the development of Torment: Tides of Numenera.
Essentially, we know what we're doing. Mostly.
Btw, can you kill everyone? Or are there some plot critical NPCs that can't die. Not that I, uh... play that way or anything.
Since we're going for a decentralized plot structure anyway, I don't think there will be any plot critical NPCs that absolutely can't be killed.
And even if there might be one or two NPCs who are critical to finishing the game, the most you'll get would be a Morrowind-like warning that you fucked up your game when you kill them, not a magic immortality mode like in Oblivion or Skyrim.
Do keep in mind that not all of our maps are designed to be combat zones, so major cities and villages will have cramped quarters that aren't intended to be fought in. But even there, if you want to, you can start combat with anyone you want. Innocent bystanders? Major quest NPCs? Merchants? Slaughter them all. Suffer the consequences.
Only children won't be killable. They'll just disappear when combat starts.
You can change that with a mod though