Warcaster is definitely a must have, tho I'd probably forget about wielding a martial weapon if you're a necro wizard, it'll do you no favor's. I posted a Necromancer build not long ago if you wanna check it out.
https://forums.larian.com/ubbthreads.php?ubb=showflat&Number=917312#Post917312Otherwise I'd go war cleric if I'm dead set on hand scythe and summoning undead, but no where near as fun as Wizard spells in my imo and multi classing is a bad idea for spellcasters, you'll miss out on powerful spells later on. There's also warlock, they can learn raising undead and can use spears and halberds.
