Since forms are generated with markdown, how can I make a partial that goes inside a modal and uses its own md file to generate a form in the partial?
Forms are actually YAML based. You will be able to pull forms into pages and even modals with Forms 2.0. This is not yet released but is available for early testing in this PR: https://github.com/getgrav/grav-plugin-form/pull/85
Ill give it a shot thanks