I want to group all uploaded Resumes under the job they were applied

[KenWhitesell]

@dwk

I want to tie job applications (resume and cover letter) to the specific job post the job seeker is applying
for.

Then you want to create a ForeignKey field in the Application model referring to the Post model.

@dwk

I want all resumes and cover letters to be uploaded in a folder named after the specific job id

See the docs for upload_to. Instead of a path, you can supply a callable that identifies the destination at runtime.