4 Imams - 4 Sunni school of thought (Jurisprudence)

[Student]

Salaamun Alayka,
Sir Joseph,

I'm extremely curious to know since 4 Sunni school of thought (Jurisprudence) precedes Ahadith Corpus, I would like to know if you have in your long research period looked/studied them and their basis? If yes:

• Were they based on the Quran?
• Has any Imam's original work survived and reached us?

Thanks,
~ Student