Precocious Apprentice gives you one second level spell once per day. At first level. Make that spell Command Undead.

Take Chain Spell as your bonus human feat.

Have high K: Religion or whatever your DM reques for you to know about and seek out undead of particular types. Or work a backstop that explains finding them. What you're looking for are Slaymates. They have an aurahat reduces the metamagic cost of necromancy spells prepared in said aura.

You want three of them to make Chain Command Undead a second level spell, which you can cast once per day. You can find them by looking for places where guardians betray and fatally neglect children; some will spontaneously arise there. People dying of Pale Wasting is another telltale sign. Slaymates inflict the disease with their bite.

You could also work up a tragic backstory about your siblings and you being betrayed by your parents or guardians and only you surviving, but one or more of your siblings coming back as Slaymates.

Command Undead is only a charm-like effect on Slaymates, but it is enough to help you win their loyalty and trust.

Get Extend Spell when you can, and two more Slaymates. Chain Extend Command Undead is CL+1 indeed minions for 2 days per CL off a single casting. Six Slaymates make this a 2nd-level spell slot.

Then, look into the Mother Cyst feat and the Necrotic Cyst spells. In combination, they can enable you to enslave living victims and force them to run up and beg for help while you make them explode in a hideous sphere of gore that does better-then-fireball damage and can infect those damaged with Necrotic Cysts you can use to control them!

Oh, and you can chain the spell that makes victims explode. And it is a necromancy spell. So Slaymates can make the chsining free.