Also, I've been looking for a cRPG with a grid-based inventory system. Kind of the Diablo 2 one.
For this part, Might and Magic has you covered, 6-8 for sure, can't recall the inventory of 3-5. And you can learn dark magic in them, not sure if you'd count them as necromancers.
M&M 3-5 have inventory lists with icons and names, no grids. From my experience the M&M are very combat-heavy, sometimes even close to grindfests, and it seems the OP puts more store in story than combat?
Has anyone here played Neverwinter Nights?
Yes, and that would have been my best recommendation. Not necessarily the official campaign, at least thematically that might not be what you're looking for (it's a bit generic and bland), but you might want to consider getting NWN in order to play fan-made modules which are often of professional quality and heavy on story-telling; and there are so many of them that you could also choose them according to gamelength - they range from short story of less than one hour to epic modules of 30 hours and more, and everything in between, whatever you prefer. And if you like the game, you can have fun with NWN's community content for years.
Neverwinter Nights has a grid-based inventory system
just like Diablo 2, only that it offers much more room (six tabs and each is about the size of the single inventory tab in Diablo 2). And it's a single-hero-RPG (even though you can have henchmen/companion joining you, but you don't control them, which might be a drawback for some but maybe not for you?).
The game also offers Prestige classes, which are like specializations for the base classes, and one specialization for wizards and sorcerers is Pale Master
, which is a kind of necromancer.
There are a few modules that are thematically related to necromancy, and where your character is involved in acts of necromancy (even though it's doesn't necessarily mean you're playing a proper necromancer in terms of class choice). Check out e.g. these ones: Revenant Deja Vu Bone Kenning I: Art of the Thanaturge Almraiven Shadewood The Breach
(In the last one you play as a - pregenerated - undead lord though, not a necromancer, and it's the only I haven't played myself, but it's supposed to be good, too)