How do I add followers to my Warlock’s patron?


Context

I’m playing a level 6 Warlock, my patron is Cthulhu (old god). I am a fan of Lovecraftian style horror, and I’d like to incorporate some of these themes in my quest. My personal quest is to create a cult of followers of Cthulhu, mostly to help me gain more forbidden knowledge but also to push the story of my character as a patron of Cthulhu. I had the opportunity recently to inflict some madness on 3 tied up initiates of a different cult who had been undergoing a stressful test to live on "air alone". I inflicted this madness using a tome my DM had given me, sharing otherworldly knowledge. I think now could be a good starting point to gain followers.

In reading other questions about creating cults, one of the things that needs to be there is authenticity. My followers need to be compelled to join me because of the horrific and terrible things I show them. I am unsure if I am powerful enough to do this yet. I want to do this according to the rules as much as I can, with less bending of rules or special treatment from my DM, since I am in a party and I still have things to do with them. I’d like to be able to gather followers sort of on the down-low without much "main quest" interference.

My Question(s)

Are there any useful spells to use that will help me recruit followers?

Are there any feats that will help me recruiting or inflicting madness?

Are there any useful spells to assist in or directly inflict madness into NPCs?

What level should I be before I can expect to reliably recruit and command followers?

Can I do this with RAW?

small caveat: I am willing, and indeed waiting, to practice necromancy. My character is chaotic neutral, but by no means am I intending for this to be static. If he becomes evil, so be it. Should be fun!