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I'm not going to pretend I know about endomorphisms (besides them being results from projection functions on the and can generate equivalent results), but before any work related to that can be started we have to fully understand how secp256k1 benefits from using them.

I found a copy of the Effective Cryptography book hosted here: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.394.3037&rep=rep1&type=pdf

So... I'm going to study that and try to see what secp256k1 does with endomorphisms.

I also set up my VScode workspace with Github integration the other day so I'm really excited about actually overhauling the codebase

Professor Lubin noted this here:
https://math.stackexchange.com/questions/3697090/endomorphism-rings-of-elliptic-curves-over-finite-fields

Perhaps this will be of some help to understand more about endomorphism, rings and EC. His example uses a diff formula than what's used by secp256k1 but for me it was helpful.